Update PullRequest to include statuses_url

Signed-off-by: Ondrej Kupka <ondra.cap@gmail.com>
Add Context field to RepoStatus

Signed-off-by: Ondrej Kupka <ondra.cap@gmail.com>
Add ListContributorsStats and ListCommitActivity for RepositoriesService
Add ListParticipation and clean up some typos
Added git tags support.
start of integration tests
travis should only run unit tests
only install ./github package with travis
add test for getting authenticated user
update Users.ListEmails to use v3 media type

This is a breaking change, but it appears that this method has been
broken for some time now and no one has complained yet, so I'm going to
assume no one is using it yet.

Notably, this is also the first (of many, I'm sure) bug I've discovered
while working on the new integration tests (#98).  Yay for better tests!