[dev][surf] Basic Address Auto-Completion

Hello

I've added a very simple url completion mode to surf, using a GtkEntryCompletion object. It only completes urls from a file just now, although I'm hoping to add history completion as well. It reads from ~/.surf/urls.txt and each address should be on a new line. Bear in mind that it isn't very clever: if you add http://example.com to urls.txt you will have to start typing http... to make it appear. I'm getting around this by only writing example.com in the file.

I think this is pretty useful, hopefully someone else might as well.

Regards
Rory McCann