Badge request: GitHub status API

[X-sam]

https://developer.github.com/v3/repos/statuses
would be useful to support it, as it allows for CI-agnostic build shields.

[paulmelnikow]

We do a badge for check state of the head commit on a pull request. So I think what probably would be useful to add is the same for branches, and if it's easy to do, for any commit hash.

[oliviertassinari]

THIS. In the project I'm working on, we have a couple of different CI tools. It would be much simpler if we could display the state of the default GitHub branch in a badge. It already aggregates all the CI tools.

[PyvesB]

We've now got a bunch of badges that can report the status of commits, branches, tags, and pull requests. For example: https://shields.io/badges/git-hub-branch-status

Will go ahead and close this issue. :)

[oliviertassinari]

I have migrated to it, but compared to CircleCI badge, it shows the latest build status:

while CircleCI badge shows the latest non-pending build status. CircleCI seems the expected behavior. The use case is to be able to, with a glance, see if there something to be worried about (broken CI branch). It would be great if we could fix this.

Issue created: #10221.