Export project contributing data as JSON

[gnrfan]

It could be useful to export a project's contributing data as JSON so other sites and apps can use the date.

It could work like this:

http://contributing.appspot.com/rails?format=json

I first thought of adding a .json extension in the URL but it could potentially clash with project names that might end with .json and project.json.json wouldn't look so good :/