Extend the definition of registered URL to deal with "compatible URLs" that aren't always identical

[tripu]

As discussed in #31.

One possible use case (of many): the URL registered with the token was https://github.com/wg/, but the URLs intended for publication are going to be in different projects, branches, subdirectories, etc. ie, the URLs that will need to be published don't match exactly the registered URL.

One option would be to go for regexes, and store them in the DB, instead of plain URLs. So for example, one could register https:\/\/github\.com\/wg\/*, or http:\/\/galactic-json\.org\/docs\/v[\d\.\-]+\/spec\.html. All kinds of issues could potentially arise related to metacharacters and regex syntax, and URL encoding…

Another (ugly) solution would be to deal with special cases (we don't expect them to be many, after all) one by one, adding logic to Symfony that would tweak checks. So for example, if the URL is a GitHub one, we more or less know how to be flexible with the URLs to be published, and what patterns we might encounter.

See also #36.

[astorije]

:-1: for regexes, times 10 if it is to be provided by users...

Since we postpone this to v(later), this leaves us time to see how things are done out there. Also, a straw poll on a team mailing-list might give us better ideas. Chances are we are worrying about a use case we actually don't have (or, that is, trying to find a generic solution to a specific problem).