Rework benchmarking script to avoid git operations

    $ git checkout master
    $ bundle exec rake benchmark:generate CORPUS=~/Downloads/samples-9
    wrote benchmark/results/samples-9-8cdb8ed4.json

    $ git checkout branch-name
    $ bx rake benchmark:generate CORPUS=~/Downloads/samples-9

    wrote benchmark/results/samples-9-8d8020dd.json

    $ bx rake benchmark:compare
REFERENCE=benchmark/results/samples-9-8cdb8ed4.json
CANDIDATE=benchmark/results/samples-9-8d8020dd.json
    LanguageA changed from 95.9% to 0.0%
    LanguageB changed from 4.0% to 99.9%
remove hash extension
Remove git dependency
Merge pull request #1516 from github/benchmarking-2

Tweaks to benchmarking stuff