add test for /repos/:repo_key/tags
add test for /repos/:repo_key/branches
corrections to _convert_branch() to match GitHub's format
add stub /repos/:repo_key/contents/:path impl
add get_repo_branch() test and make it pass
add test for get_repo_commit()
kill maxDiff overrides leftover from debugging
add test for get_repos_tag()
add tests for error cases for new APIs
convert a couple of list comprehensions to generator expressions
note that /repos/:repo_key/tags/:tag_name API is RestfulGit-specific; see #59
compare /git/commits against GitHub's output

apply .rstrip() to commit messages to match GitHub
per GitHub, all UTC (aka Z for Zulu Time) all the time
test get_tag_works() against GitHub output