Implementation of a new medialib backend

by Cippo for XMMS2

XMMS2 is a music player with a media library to keep track of your songs. Currently SQlite is used to store the media info, but this has some drawbacks, most notably in speed. If a specialized backend was used instead of SQlite you could exploit the fact that entries into the medialib share alot of similarities. That way you would get a faster media library and a reduced footprint.