Improved Search Client

[ciaranm]

Paludis currently has a fairly primitive search client, inquisitio. There is lots of room for improving it:

• More flexibility in searching. It should allow arbitrarily complex queries (find me packages with GPL-2 in LICENSE that depend upon libfoo). Maybe 'find' is a good model for an interface for this, maybe you can think of something better.
• More flexibility in output format.
• Performance. Look into adding an optional descriptions cache (on a per repository basis) to avoid doing a full tree scan.

There's lots of room for creativity here. Think about how you think when you're trying to find packages.