Support Statistics API

[dsheets]

See https://developer.github.com/v3/repos/statistics/ for @amirmc's project.

• Get contributors list with additions, deletions, and commit counts (contributor api binding #114)
• Get the last year of commit activity data
• Get the number of additions and deletions per week
• Get the weekly commit count for the repository owner and everyone else
• Get the number of commits per hour in each day

[tmcgilchrist]

Think I've covered all these endpoints and this can be closed @Aaylor.