Store Requires/Provides/Obsoletes

The old style requires/provides/obsoletes is practically useless even as a displayed purpose. They should probably be stored for completeness sake.

The new style *_dist requirements are actually useful and should be stored, ideally in a form that makes it possible to do interesting things with them.

We should likely attempt to do an approximation of requires_dist via setuptools. Will need to see how likely this is but hopefully we can do something useful here.