Data file code ok; more docs

Some of the data file handling code has been written. This includes the low level stuff for reading and writing to files. The next logical step is to formalize a data structure for pcm to internally store the data. Basic documentation for this has been added to the Docs section.

After the internal data storage stuff is taken care of, and possibly after some more graphics code (namely thumbnail handling), it'll actually be time to start working on the GTK+ GUI. Yay! ;-)