don't put the api version in the URIs

For the sake of restfulness, don't put the API version number in the
URL.
Instead, use the HTTP Accept token.

See http://pivotallabs.com/api-versioning/
And GitHub's API: http://developer.github.com/v3/media/
Merge pull request #8 from dmathieu/api_versioning

Don't use URIs to version the API