New hash_append robust container hash function framework:
* is_contiguous_hashable trait identifies optimizable types
* hash_append() function overloads for basic types:
  - scalars, floats
  - array, C array
  - pair, tuple
  - boost array and tuple (if configured)
* Provided Spooky hash wrapper for use with hash_append
* Use hash_append in hardened_hash and other places
* New Utility meta functions for working with variadics:
  - static_and
  - static_sum
* Added type_name utility function for diagnostics
* hash_metrics suite of functions to evalulate hash functions
* Test suites to measure hash function performance
* Various fixes
Fix assert invariant in Peers::close_all
More robustly validate signature inputs, closes #313
Don't create peer doors in standalone mode
Autobridging hooks and cleanups:

- Detect when we should autobridge and get bridge books.
- Move applyOffer from STAmount into the OfferCreate transactor.
Must set flags before signing validation.
Sub in std::array for boost::array and beast::FixedArray
Force BOOST_ASIO_HAS_STD_ARRAY to 1
for the clang / gcc libstdc++ 4.8 combination
Remove unused legacy code
Add bg_threads and high_threads RocksDB tunables
Configuration file improvements:
* Set default node_db to RocksDB from HyperlevelDB, to match gateway
  appliances and Ripple Labs server configurations.
* Set some rpc_startup options to reduce logging and save disk space.
* More sensible documentation regarding WebSocket SSL directives

Signed-off-by: The Doctor <drwho@virtadpt.net>