Split up the Resource interface into GetResource, PostResource, etc. Then
modified the response writer so that it calls Get/Post/etc if implemented,
otherwise it sets code, data = 405, "". If they want a more sophisticated
error, they have to implement it in the method.

Deleted http.go as it was not relevant any more.
forgot about function arguments as Resource interface. Had to change it to an
interface{} because AFAIK there isn't a way to have partial interfaces. This
makes declaring resources a bit simpler, but one could theoretically add a
resource with no methods at all. It would obviously 405, but it could be a
problem for a particularly forgetful developer.