Allow for more granular searches of URLs

[toolness]

In toolness/weblitmapper#22, I'd like to show users a list of other resources tagged on the same domain, but there doesn't seem to be an easy way to do this with the MakeAPI. If there were a urlPrefix query term, analogous to the existing tagPrefix term, that would make it possible... Another alternative would be to actually parse the URLs and index them by full domain name and/or TLD.

[toolness]

Actually, I just realized there's a "hack" we can use to get around this--the web lit mapper can add special application-specific tags like urldomain-foo.org to weblit resources and then do a search for them to easily find other resources on a particular domain.