Summary:
Introduce TableOptions section and support BlockBasedTable in RocksDB
options file.  A TableOptions section has the following format:

  [TableOptions/<FactoryClassName> "<ColumnFamily Name>"]

which includes information about its TableFactory class and belonging
column family.  Below is an example TableOptions section of a
BlockBasedTableOptions that belongs to the default column family:

  [TableOptions/BlockBasedTable "default"]
    format_version=0
    whole_key_filtering=true
    block_size_deviation=10
    block_size=4096
    block_restart_interval=16
    filter_policy=nullptr
    no_block_cache=false
    checksum=kCRC32c
    cache_index_and_filter_blocks=false
    index_type=kBinarySearch
    hash_index_allow_collision=true
    flush_block_policy_factory=FlushBlockBySizePolicyFactory

Currently, Cache-type options (i.e., block_cache and block_cache_compressed)
are not supported.

Test Plan: options_test

Reviewers: igor, anthony, IslamAbdelRahman, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D48435