Benchmark additions and enhancements

Original [issue 238](https://code.google.com/p/leveldb/issues/detail?id=238) created by HighlandSun on 2014-06-09T10:21:11.000Z:

I've added benchmark drivers for BerkeleyDB, LMDB, Sophia, TokuDB, Basho LevelDB, HyperLevelDB, and RocksDB. Also merged a few features from the RocksDB source tree. Code is available here https://github.com/hyc/leveldb/tree/benches

Using a unified benchmark framework like this gives us directly comparable results for each of these K/V storage engines.

What version of the product are you using? On what operating system?
1.17 Linux

Please provide any additional information below.