db_bench: sanity check on compression ratio

Summary: as requested by mark

Test Plan: make release

Reviewers: sdong, haobo

Reviewed By: haobo

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19221
Fix some entries in HISTORY.md

Summary:
Add one entry to HISTORY.md that is failed to be added.
Move two other ones to the right location.

Test Plan: Only document

Reviewers: haobo, ljin

Subscribers: dhruba, yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D19233
[RocksDB] history change for 3.2

Summary: as title

Test Plan: none

Reviewers: ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19239
db_bench: measure the real latency of write/delete

Summary: as title

Test Plan: make release

Reviewers: haobo, sdong, yhchiang

Reviewed By: yhchiang

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19227
[RocksDB] allow LDB tool to have customized key formatter

Summary: Currently ldb tool dump keys either in ascii format or hex format - neither is ideal if the key has a binary structure and is not readable in ascii. This diff also allows LDB tool to be customized in ways beyond DB options.

Test Plan: verify that key formatter works with some simple db with binary key.

Reviewers: sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19209
Update README.md

typo
Fix a rapidjson compile error in mac.

Summary:
This diff fixes the following compilation error in mac.
  ./third-party/rapidjson/reader.h:422:31: error: comparison of constant 256 with expression of type 'Ch' (aka 'char') is always true
        [-Werror,-Wtautological-constant-out-of-range-compare]
                                  if ((sizeof(Ch) == 1 || e < 256) && escape[(unsigned char)e])
                                                          ~ ^ ~~~
  1 error generated.

Test Plan: make db_test

Reviewers: haobo, sdong, igor, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19245
Fix compile error caused in LDB tool

Summary:
Fixed the following compile error.
    tools/reduce_levels_test.cc:89:31: error: no matching function for call to 'InitFromCmdLineArgs'
      LDBCommand* level_reducer = LDBCommand::InitFromCmdLineArgs(args);
                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ./util/ldb_cmd.h:56:22: note: candidate function not viable: requires 3 arguments, but 1 was provided
      static LDBCommand* InitFromCmdLineArgs(
                         ^
    ./util/ldb_cmd.h:62:22: note: candidate function not viable: requires 4 arguments, but 1 was provided
      static LDBCommand* InitFromCmdLineArgs(
                         ^
    1 error generated.

Test Plan:
make reduce_levels_test
./reduce_levels_test

Reviewers: haobo, ljin, sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19251
Fix compile error in reduce_levels_test.

Summary:
Fixed the following compile error.
    tools/reduce_levels_test.cc:89:31: error: no matching function for call to 'InitFromCmdLineArgs'
      LDBCommand* level_reducer = LDBCommand::InitFromCmdLineArgs(args);
                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ./util/ldb_cmd.h:56:22: note: candidate function not viable: requires 3 arguments, but 1 was provided
      static LDBCommand* InitFromCmdLineArgs(
                         ^
    ./util/ldb_cmd.h:62:22: note: candidate function not viable: requires 4 arguments, but 1 was provided
      static LDBCommand* InitFromCmdLineArgs(
                         ^
    1 error generated.

Test Plan:
make reduce_levels_test
./reduce_levels_test

Reviewers: haobo, sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19251
Revert the default setting of InitFromCmdLineArgs().

Summary:
Revert the default setting of InitFromCmdLineArgs() as all the callers
currently provide full set of arguments.

Test Plan:
make reduce_levels_test
./reduce_levels_test

Reviewers: haobo, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19257