Accept strings as well as Label objects (#202)

This should be more generic, but it's a wig work to do it
everywhere. Let's keep that in mind for V2.
Acknowledge lack of test coverage in the old Download API
Implement equality comparison of CompletableGithubObject (#201)
Add 'author' to 'Repository.get_commits' (#204)
Fix tests broken by previous commit
Fix doc
First step of implementation of Repository.get_stats_xxx (#203)
Fix copyright headers
Finish .../stats/... (#203)
Fix tests for Python 2.5 and 2.6
Update readme for #203
Merge branch 'develop'
Publish version 1.21.0
Merge pull request #1 from jacquev6/master

latest from upstream