Supports the updated starring API as mentioned in issue #188.

There is now a new struct called StarredRepository which holds a Repository and the new `starred_at` timestamp.
For now there is a special media type to request the new API. I've added a TODO for it to be deleted when the new API fully launches.

There's no way of serializing/requesting an empty required_contexts that
is needed for bypassing the commit status checks for the ref.

It's a breaking change but will allow to serialize an empty array and
omit empty value as expected.

Fixes #185.

Memberships API is now official.

https://developer.github.com/changes/2014-09-16-finalizing-the-organization-and-team-membership-apis/

Fixes #192

Deployments API is now official.

https://developer.github.com/changes/2014-11-25-the-deployments-api-is-official/

Fixes #189.

Both have been deprecated.

Fixes #190.

- AddTeamMember: https://developer.github.com/v3/orgs/teams/#add-team-member
- RemoveTeamMember: https://developer.github.com/v3/orgs/teams/#remove-team-member

Also:
 - add PingHook to RepositoriesService
 - move ListServiceHooks to Client, since hooks are no longer just for
   repos.  Leave behind Repositories.ListServiceHooks for backwards
   compatibility

Fixes #178

The client_id and client_secret URL variables,
containing sensitive app information, are leaked
to users if the Go error is returned to them. To
prevent this, sanitizeURL redacts the fields from
ErrorResponse's Error method. Therefore making the
error message safe to expose to users.

(not added to AUTHORS - Google owns copyright)

RepositoryListByOrgOptions doesn't have a `Sort` field

As per https://developer.github.com/v3/pulls/#list-pull-requests

Renamed test method

Changed from PatchUrl to PatchURL

The RepositoryContent struct doesn't quite map to the API because it is
missing a download link.  This link is very useful because while the API
doesn't allow large files to be downloaded, the link allows the raw
files to be downloaded outside the API.

The issue is that the JSON tags on the contents struct were wrong.  They
were missing the underscore.

Unfortunately this is a breaking change, and having a pointer to a slice
is not very common, but is needed in this case to allow clearing an
issue's labels.

Fixes #181

Fixes references to depreciated goauth2 libaray and replaces example
with the recomended oauth2 implimentation.

This integer exposes the number of comments that have been posted for that commit on GitHub.

It is documented at https://developer.github.com/v3/repos/commits/.

https://developer.github.com/v3/repos/releases/#create-a-release

Fixes #159