Docs

Created by: juaristi

I documented the hashing functions (defined in hashfile.c) using GTK-Docs, which is already built into the Makefiles, and produces beautiful HTML output. Looks like some of these functions are dependent on the underlying cryptographic engine (e.g. libnettle) so I documented these on the header file (libwget.h), since there are more than one implementations. All the others are documented in the source itself (hashfile.c).

Please review my changes, specially the accuracy/correctness of the terms used. If no one complains, I'll push them next week.