Add a way to add responses to documentation

You can add a predefined JSON response by entering
"json(:resource_name)" in the docstring. This will then be replaced
with the resource with the same name, found in
lib/travis/api/app/endpoint/documentation/resources.rb.
Add responses to repository endpoints
Update docs style to look more like the main docs site
Add favicon
Merge pull request #25 from henrikhodne/add-responses-to-documentation

Add responses to documentation
Update example payloads