Remove obsolete classes, disable unused code, and tidy up:
* Removed MultiSocket. Code that previously used the MultiSocket now uses
  a combination of boost::asio coroutines and CRTP.
* Sitefiles headers rolled up and directory flattened.
* Disabled Sitefiles use of deprecated HTTPClient.
* Validators headers tidied up.
* Disabled Validators use of deprecated HTTPClient.
Remove unused and obsolete classes and tidy up:
Many classes required to support type-erasure of handlers and boost::asio
types are now obsolete, so these classes and files are removed:
HTTPClientType, FixedInputBuffer, PeerRole, socket_wrapper,
client_session, basic_url, abstract_socket, buffer_sequence, memory_buffer,
enable_wait_for_async, shared_handler, wrap_handler, streambuf,
ContentBodyBuffer, SSLContext, completion-handler based handshake detectors.
These structural changes are made:
* Some missing includes added to headers
* asio module directory flattened
Remove obsolete RPCServerHandler:
This removes the legacy RPCServerHandler, which has been replaced by the
asynchronous RPC-HTTP/S server and corresponding RPCHTTPHandler.
Refactor the structure of ServerHandler:
This is a cleanup to the structure of the sources.
* Rename to ServerHandler
* Move private implementation declaration to separate header
* De-inline function definitions in the class declaration.
Reduce Beast public interface and eliminate unused code:

Beast includes a lot of code for encapsulating cross-platform differences
which are not used or needed by rippled. Additionally, a lot of that code
implements functionality that is available from the standard library.

This moves away from custom implementations of features that the standard
library provides and reduces the number of platform-specific interfaces
andfeatures that Beast makes available.

Highlights include:
* Use std:: instead of beast implementations when possible
* Reduce the use of beast::String in public interfaces
* Remove Windows-specific COM and Registry code
* Reduce the public interface of beast::File
* Reduce the public interface of beast::SystemStats
* Remove unused sysctl/getsysinfo functions
* Remove beast::Logger
Reduce RippleD dependencies on Beast:
* Use static_assert where appropriate
* Use std::min and std::max where appropriate
* Simplify RippleD error reporting
* Remove use of beast::RandomAccessFile
Squelch some warnings in rippled and third-party code.
Adjust paths and costs in Pathfinder.
Update SQLite to 3.8.7:
sha1: 3e23079f062fc06705eead4db108ee429878b532
Squashed 'src/rocksdb2/' changes from 25888ae..1fdd726

1fdd726 Hotfix RocksDB 3.5
d67500a Add `make install` to Makefile in 3.5.fb.
4cb631a update HISTORY.md
cfd0946 comments about the BlockBasedTableOptions migration in Options
REVERT: 25888ae Merge pull request #329 from fyrz/master
REVERT: 89833e5 Fixed signed-unsigned comparison warning in db_test.cc
REVERT: fcac705 Fixed compile warning on Mac caused by unused variables.
REVERT: b3343fd resolution for java build problem introduced by 5ec53f3edf62bec1b690ce12fb21a6c52203f3c8
REVERT: 187b299 ForwardIterator: update prev_key_ only if prefix hasn't changed
REVERT: 5ec53f3 make compaction related options changeable
REVERT: d122e7b Update INSTALL.md
REVERT: 986dad0 Merge pull request #324 from dalgaaf/wip-da-SCA-20140930
REVERT: 8ee75dc db/memtable.cc: remove unused variable merge_result
REVERT: 0fd8bbc db/db_impl.cc: reduce scope of prefix_initialized
REVERT: 676ff7b compaction_picker.cc: remove check for >=0 for unsigned
REVERT: e55aea5 document_db.cc: fix assert
REVERT: d517c83 in_table_factory.cc: use correct format specifier
REVERT: b140375 ttl/ttl_test.cc: prefer prefix ++operator for non-primitive types
REVERT: 43c789c spatialdb/spatial_db.cc: use !empty() instead of 'size() > 0'
REVERT: 0de452e document_db.cc: pass const parameter by reference
REVERT: 4cc8643 util/ldb_cmd.cc: prefer prefix ++operator for non-primitive types
REVERT: af8c2b2 util/signal_test.cc: suppress intentional null pointer deref
REVERT: 33580fa db/db_impl.cc: fix object handling, remove double lines
REVERT: 873f135 db_ttl_impl.h: pass func parameter by reference
REVERT: 8558457 ldb_cmd_execute_result.h: perform init in initialization list
REVERT: 063471b table/table_test.cc: pass func parameter by reference
REVERT: 93548ce table/cuckoo_table_reader.cc: pass func parameter by ref
REVERT: b8b7117 db/version_set.cc: use !empty() instead of 'size() > 0'
REVERT: 8ce050b table/bloom_block.*: pass func parameter by reference
REVERT: 53910dd db_test.cc: pass parameter by reference
REVERT: 68ca534 corruption_test.cc: pass parameter by reference
REVERT: 7506198 cuckoo_table_db_test.cc: add flush after delete
REVERT: 1f96330 Print MB per second compaction throughput separately for reads and writes
REVERT: ffe3d49 Add an instruction about SSE in INSTALL.md
REVERT: ee1f3cc Package generation for Ubuntu and CentOS
REVERT: f0f7955 Fixing comile errors on OS X
REVERT: 99fb613 remove 2 space linter
REVERT: b2d64a4 Fix linters, second try
REVERT: 747523d Print per column family metrics in db_bench
REVERT: 56ebd40 Fix arc lint (should fix #238)
REVERT: 637f891 Merge pull request #321 from eonnen/master
REVERT: 827e31c Make test use a compatible type in the size checks.
REVERT: fd5d80d CompactedDB: log using the correct info_log
REVERT: 2faf49d use GetContext to replace callback function pointer
REVERT: 983d2de Add AUTHORS file. Fix #203
REVERT: abd70c5 Merge pull request #316 from fyrz/ReverseBytewiseComparator
REVERT: 2dc6f62 handle kDelete type in cuckoo builder
REVERT: 8b8011a Changed name of ReverseBytewiseComparator based on review comment
REVERT: 389edb6 universal compaction picker: use double for potential overflow
REVERT: 5340484 Built-in comparator(s) in RocksJava
REVERT: d439451 delay initialization of cuckoo table iterator
REVERT: 94997ea reduce memory usage of cuckoo table builder
REVERT: c627595 improve memory efficiency of cuckoo reader
REVERT: 581442d option to choose module when calculating CuckooTable hash
REVERT: fbd2daf CompactedDBImpl::MultiGet() for better CuckooTable performance
REVERT: 3c68006 CompactedDBImpl
REVERT: f7375f3 Fix double deletes
REVERT: 21ddcf6 Remove allow_thread_local
REVERT: fb4a492 Merge pull request #311 from ankgup87/master
REVERT: 611e286 Merge branch 'master' of https://github.com/facebook/rocksdb
REVERT: 0103b44 Merge branch 'master' of ssh://github.com/ankgup87/rocksdb
REVERT: 1dfb7bb Add block based table config options
REVERT: cdaf44f Enlarge log size cap when printing file summary
REVERT: 7cc1ed7 Merge pull request #309 from naveenatceg/staticbuild
REVERT: ba6d660 Resolving merge conflict
REVERT: 51eeaf6 Addressing review comments
REVERT: fd7d3fe Addressing review comments (adding a env variable to override temp directory)
REVERT: cf7ace8 Addressing review comments
REVERT: 0a29ce5 re-enable BlockBasedTable::SetupForCompaction()
REVERT: 55af370 Remove TODO for checking index checksums
REVERT: 3d74f09 Fix compile
REVERT: 53b0039 Fix release compile
REVERT: d0de413 WriteBatchWithIndex to allow different Comparators for different column families
REVERT: 57a32f1 change target_file_size_base to uint64_t
REVERT: 5e6aee4 dont create backup_input if compaction filter v2 is not used
REVERT: 49b5f94 Merge pull request #306 from Liuchang0812/fix_cast
REVERT: 787cb4d remove cast, replace %llu with % PRIu64
REVERT: a7574d4 Update logging.cc
REVERT: 7e0dcb9 Update logging.cc
REVERT: 57fa3cc Merge pull request #304 from Liuchang0812/fix-check
REVERT: cd44522 Merge pull request #305 from Liuchang0812/fix-logging
REVERT: 6a031b6 remove unused variable
REVERT: 4436f17 fixed #303: replace %ld with % PRId64
REVERT: 7a1bd05 Merge pull request #302 from ankgup87/master
REVERT: 423e52c Merge branch 'master' of https://github.com/facebook/rocksdb
REVERT: bfeef94 Add rate limiter
REVERT: 32f2532 Print compression_size_percent as a signed int
REVERT: 976caca Skip AllocateTest if fallocate() is not supported in the file system
REVERT: 3b897cd Enable no-fbcode RocksDB build
REVERT: f445947 RocksDB: Format uint64 using PRIu64 in db_impl.cc
REVERT: e17bc65 Merge pull request #299 from ankgup87/master
REVERT: b93797a Fix build
REVERT: adae3ca [Java] Fix JNI link error caused by the removal of options.db_stats_log_interval
REVERT: 90b8c07 Fix unit tests errors
REVERT: 51af7c3 CuckooTable: add one option to allow identity function for the first hash function
REVERT: 0350435 Fixed a signed-unsigned comparison in spatial_db.cc -- issue #293
REVERT: 2fb1fea Fix syncronization issues
REVERT: ff76895 Remove some unnecessary constructors
REVERT: feadb9d fix cuckoo table builder test
REVERT: 3c232e1 Fix mac compile
REVERT: 54cada9 Run make format on PR #249
REVERT: 27b22f1 Merge pull request #249 from tdfischer/decompression-refactoring
REVERT: fb6456b Replace naked calls to operator new and delete (Fixes #222)
REVERT: 5600c8f cuckoo table: return estimated size - 1
REVERT: a062e1f SetOptions() for memtable related options
REVERT: e4eca6a Options conversion function for convenience
REVERT: a7c2094 Merge pull request #292 from saghmrossi/master
REVERT: 4d05234 Merge branch 'master' of github.com:saghmrossi/rocksdb
REVERT: 60a4aa1 Test use_mmap_reads
REVERT: 94e43a1 [Java] Fixed 32-bit overflowing issue when converting jlong to size_t
REVERT: f9eaaa6 added include for inttypes.h to fix nonworking printf statements
REVERT: f090575 Replaced "built on on earlier work" by "built on earlier work" in README.md
REVERT: faad439 Fix #284
REVERT: 49aacd8 Fix make install
REVERT: acb9348 [Java] Include WriteBatch into RocksDBSample.java, fix how DbBenchmark.java handles WriteBatch.
REVERT: 4a27a2f Don't sync manifest when disableDataSync = true
REVERT: 9b8480d Merge pull request #287 from yinqiwen/rate-limiter-crash-fix
REVERT: 28be16b fix rate limiter crash #286
REVERT: 04ce1b2 Fix #284
REVERT: add22e3 standardize scripts to run RocksDB benchmarks
REVERT: dee91c2 WriteThread
REVERT: 540a257 Fix WAL synced
REVERT: 24f034b Merge pull request #282 from Chilledheart/develop
REVERT: 49fe329 Fix build issue under macosx
REVERT: ebb5c65 Add make install
REVERT: 0352a9f add_wrapped_bloom_test
REVERT: 9c0e66c Don't run background jobs (flush, compactions) when bg_error_ is set
REVERT: a9639bd Fix valgrind test
REVERT: d1f24dc Relax FlushSchedule test
REVERT: 3d9e6f7 Push model for flushing memtables
REVERT: 059e584 [unit test] CompactRange should fail if we don't have space
REVERT: dd641b2 fix RocksDB java build
REVERT: 53404d9 add_qps_info_in cache bench
REVERT: a52cecb Fix Mac compile
REVERT: 092f97e Fix comments and typos
REVERT: 6cc1286 Added a few statistics for BackupableDB
REVERT: 0a42295 Fix SimpleWriteTimeoutTest
REVERT: 06d9862 Always pass MergeContext as pointer, not reference
REVERT: d343c3f Improve db recovery
REVERT: 6bb7e3e Merger test
REVERT: 88841bd Explicitly cast char to signed char in Hash()
REVERT: 5231146 MemTableOptions
REVERT: 1d284db Addressing review comments
REVERT: 55114e7 Some updates for SpatialDB
REVERT: 171d4ff remove TailingIterator reference in db_impl.h
REVERT: 9b0f7ff rename version_set options_ to db_options_ to avoid confusion
REVERT: 2d57828 Check stop level trigger-0 before slowdown level-0 trigger
REVERT: 659d2d5 move compaction_filter to immutable_options
REVERT: 048560a reduce references to cfd->options() in DBImpl
REVERT: 011241b DB::Flush() Do not wait for background threads when there is nothing in mem table
REVERT: a2bb7c3 Push- instead of pull-model for managing Write stalls
REVERT: 0af157f Implement full filter for block based table.
REVERT: 9360cc6 Fix valgrind issue
REVERT: 02d5bff Merge pull request #277 from wankai/master
REVERT: 88a2f44 fix comments
REVERT: 7c16e39 Merge pull request #276 from wankai/master
REVERT: 8237738 replace hard-coded number with named variable
REVERT: db8ca52 Merge pull request #273 from nbougalis/static-analysis
REVERT: b7b031f Merge pull request #274 from wankai/master
REVERT: 4c2b1f0 Merge remote-tracking branch 'upstream/master'
REVERT: a5d2863 typo improvement
REVERT: 9f8aa09 Don't leak data returned by opendir
REVERT: d1cfb71 Remove unused member(s)
REVERT: bfee319 sizeof(int*) where sizeof(int) was intended
REVERT: d40c1f7 Add missing break statement
REVERT: 2e97c38 Avoid off-by-one error when using readlink
REVERT: 40ddc3d add cache bench
REVERT: 9f1c80b Drop column family from write thread
REVERT: 8de151b Add db_bench with lots of column families to regression tests
REVERT: c9e419c rename options_ to db_options_ in DBImpl to avoid confusion
REVERT: 5cd0576 Fix compaction bug in Cuckoo Table Builder. Use kvs_.size() instead of num_entries in FileSize() method.
REVERT: 0fbb3fa fixed memory leak in unit test DBIteratorBoundTest
REVERT: adcd253 fix asan check
REVERT: 4092b7a Merge pull request #272 from project-zerus/patch-1
REVERT: bb6ae0f fix more compile warnings
REVERT: 6d31441 Merge pull request #271 from nbougalis/cleanups
REVERT: 0cd0ec4 Plug memory leak during index creation
REVERT: 4329d74 Fix swapped variable names to accurately reflect usage
REVERT: 45a5e3e Remove path with arena==nullptr from NewInternalIterator
REVERT: 5665e5e introduce ImmutableOptions
REVERT: e0b99d4 created a new ReadOptions parameter 'iterate_upper_bound'
REVERT: 51ea889 Fix travis builds
REVERT: a481626 Relax backupable rate limiting test
REVERT: f7f973d Merge pull request #269 from huahang/patch-2
REVERT: ef5b384 fix a few compile warnings
REVERT: 2fd3806 Merge pull request #263 from wankai/master
REVERT: 1785114 delete unused Comparator
REVERT: 1b1d961 update HISTORY.md
REVERT: 703c3ea comments about the BlockBasedTableOptions migration in Options
REVERT: 4b5ad88 Merge pull request #260 from wankai/master
REVERT: 19cc588 change to filter_block std::unique_ptr support RAII
REVERT: 9b976e3 Merge pull request #259 from wankai/master
REVERT: 5d25a46 Merge remote-tracking branch 'upstream/master'
REVERT: dff2b1a typo improvement
REVERT: 343e98a Reverting import change
REVERT: ddb8039 RocksDB static build Make file changes to download and build the dependencies .Load the shared library when RocksDB is initialized

git-subtree-dir: src/rocksdb2
git-subtree-split: 1fdd726a8254c13d0c66d8db8130ad17c13d7bcc
Update src/rocksdb2 to rocksdb-3.5.1:
Merge commit 'c168d54495d7d7b84639514f6443ad99b89ce996' into develop
Update rocksdb unity file
Set version to 0.26.4-rc4