Support selecting which commands to execute for benchmark

Move textmatching to it's own sub-project to make it easier to grab for
use in benchmark config.
Benchmark profiles for file text-replacement

Prompted by this StackOverflow question:

...which initally reported the BFG was slower than
git-filter-branch. That was later retracted, but I had a few ideas
about how maybe we could go faster, so gotta get those benchmarks
in first.