Add some benchmarks

As it stands, Sophist is significantly faster than LevelDOWN in all
areas other than transactions (batches).  I believe this to be due to
Sophist writing data asynchronously while in a transaction, but I'm not
100% sure.

This will change for the next release :)
refactor "closing" test
Add #deleteSync
Add synchronous benchmarks
Merge branch 'master' into wip-remove-nan

* master:
  Add synchronous benchmarks
  Add #deleteSync
  refactor "closing" test
  Add some benchmarks

Conflicts:
	src/delete.h
	src/sophist.cc
	src/sophist.h
typo