[Inkscape-devel] URI class

Well... to get some stuff cleaned up, I've started a bit of tune-up on the URI class. I've added a few methods, but also added Doxygen comments.

The latter might make a difference, as I'm counting on the class behaving the way I've described, so checking things over to be sure the docs are proper and in sync would be helpful.

Of course, if anyone cares, they can also check to see if I did any late-night careless stuff. (Oh, and diff with ignoring whitespace).