any_url usability improvements

[buhman]

21:17:37 sudokode buhman: shame you can't GET a uuid
21:17:49 sudokode that would simplify this

20:50:11 sudokode gotcha. yeah that makes it much cleaner
20:50:27 sudokode tries label, then short, then long
20:50:32 sudokode for finding a pasteid

I'm not convinced on adding a GET url route for uuids, but any_url logic does make it difficult for API consumers to figure out which identifier was considered optimal for that paste.

I'm not really sure how to solve this in a clean way, other than by giving some kind of X-Paste-Key hint, or adding some kind of key field to the response body.