initial bench and generate command structure
moar bench package
fix basic parallel benchmark
add benchmarks using Benchmark framework
add bench sub-package
move bench package to bench/cmd/bolt/bench
Add 'bolt bench'.

This commit adds a flexible benchmarking tool to the 'bolt' CLI. It allows
the user to separately specify the write mode and read mode (e.g. sequential
random, etc). It also allows the user to isolate profiling to either the
read or the writes.

Currently the bench tool only supports "seq" read and write modes. It also
does not support streaming of Bolt counters yet.

Fixes #95.

/cc @snormore