DELETE: Added new semantic: resource collection deletion.

If a client wants to remove every resource in a collection, say `/posts` or `/logs`, there is no current defined semantics for doing a bulk delete.

Of course, the client can make multiple *DELETE* for each resource in the collection, or even make a DELETE to an URL like `/logs/1,2,3,7,8,9,10`, but those solutions don't work right when one have zillions of items in a collection.

This commit add semantics to *DELETE* an entire collection by using the collection URL.

Hope you like it.

pd. hope you find the duck so you only can bikeshed the commit and not cancel it completelly :D (just joking)