Summary:
This diff includes an implementation of CompactionFilter that allows
users to write CompactionFilter in Lua.  With this ability, users can
dynamically change compaction filter logic without requiring building
the rocksdb binary and restarting the database.

To compile, WITH_LUA_PATH must be specified to the base directory
of lua.
Closes https://github.com/facebook/rocksdb/pull/1478

Differential Revision: D4150138

Pulled By: yhchiang

fbshipit-source-id: ed84222