Feature: Added token support to CircleCI badges

[krak3n]

This PR adds CircleCI token support in the same vein as the token feature on CodeCov allowing serving of private CircleCI builds.

See regex here: http://regexr.com/3b2v7

[espadrine]

I'm confused. Was having a default token never necessary?

Here's what I was told back then: #348 (comment)

[krak3n]

The token is used to query the circle REST API and isn't be needed for public project build states. If the project is private then you need a token to access the REST API to get the build state of the project.

So the example project is public and thus works without a token:

curl https://circleci.com/api/v1/project/BrightFlair/PHP.Gt\?limit\=1\&filter\=completed -H "Accept:application/json"

https://github.com/BrightFlair/PHP.Gt

[espadrine]

So, what if the example project is private? Will existing badges stop working?

[krak3n]

@espadrine at the moment I think that the token is ignored, public projects wouldn't break if the example repo became private. For example I can put a random circle token on the end and the API responds normally:

curl https://circleci.com/api/v1/project/BrightFlair/PHP.Gt\?limit\=1\&filter\=completed\&circle-token\=foo -H "Accept:application/json"

Basically all this PR does is remove the ignored token by default and allow the user to pass their own token in for private projects.

[maletor]

Perfecto!

[espadrine]

Thanks for contributing!