Add support for commit status contexts.

[farmdawgnation]

The GitHub status API now supports the concept of optional contexts for commit statuses. It would be useful to be able to add those from the Java API for the benefit of things like the GitHub Pull Request builder.

I'm going to try and find some time in the next week to actually work on this. If someone else starts tackling it before I get around to it, please comment here so we're not duplicating work! :)

[suryagaddipati]

Are you referring to this https://developer.github.com/v3/repos/statuses/#get-the-combined-status-for-a-specific-ref

Given that GHE always lags behind. It would be nice to make sure that change works both for GHE and public api.

[farmdawgnation]

I was talking about the counterpart for that which creates a status with an additional context parameter in the JSON POST body. That said implementing the retrieval of those should happen too. The context parameter is optional, so the change wouldn't break GHE support of statuses. They just can't take advantage of the feature until it's released on GHE.

That said. It may have already been. This feature came out a few months ago if I recall.

[suryagaddipati]

Oh ok.I 've noticed that GHE usually lags 7-8 months.

I've opened a pr for adding context
#97

[farmdawgnation]

Awesome! Thanks!

[farmdawgnation]

Pretty sure this should have been closed with the merging of #97 - not sure why it wasn't.