Respond with 422 if /auth/github does not get a token

Fix #77
Merge pull request #78 from travis-ci/hh-auth-github-422

Respond with 422 if /auth/github does not get a token
Only allow XML response if repo has a build
Only allow image responses for repositories
Handle race condition with creating users more nicely
Handle JSON parsing errors
Merge pull request #80 from travis-ci/hh-image-responder-repo

Only allow image responses for repositories
Merge pull request #82 from travis-ci/hh-handle-json-parsererrors

Handle JSON parsing errors
Merge pull request #81 from travis-ci/hh-auth-race-condition

Handle race condition with creating users more nicely
Move /jobs/:id/cancel to /jobs
Merge pull request #83 from travis-ci/hh-cancel-job-wrong-namespac

Move /jobs/:id/cancel to /jobs
Merge pull request #79 from travis-ci/hh-xml-responder-nil-last-build

Only allow XML response if repo has a build
force deploy