[dmd-internals] GitHub commit status API

[Brad Roberts]

The changes aren't quite in production yet but it's about 95% ready.  Here's three example pull requests with their
statuses set as of a little while ago:

passed:
  https://github.com/D-Programming-Language/phobos/pull/773

work in progress:
  (since finished, but the status hasn't been changed to reflect that yet)
  https://github.com/D-Programming-Language/phobos/pull/768

work complete, with failures:
  https://github.com/D-Programming-Language/phobos/pull/750

It will also show "Pending: #" if there's any left that haven't started yet.  I don't have one of those setup right now.

Before I turn this on.. does anyone strongly object to the last updated field becoming meaningless?  The github guys
aren't likely to change the current behavior that a status update is an event that causes the date to move forward.  If
I don't hear any major objections, I'm going to turn it on for all of the phobos builds late tomorrow night or saturday
some time.

Any thoughts on the descriptive text?  The part that's determined by the api is what's between the dash and the open
paren around Details.

Later,
Brad