During library creation add a special playlist

The special playlist - .global - will hold all media elements in the
library. Anything added to another playlist will be automatically added
to the .global list as well.

Signed-off-by: Alex Waterman <imNotListening@gmail.com>
Add special bucket data structure for holding playlists

The goal is to have fast access times while using packed strings
memory mapped from a disk. Therefor we cannot use malloc() or anything
like that. For more info about the playlist buckets see bucket.c.

Signed-off-by: Alex Waterman <imNotListening@gmail.com>
Merge branch 'library-dev'

Conflicts:
	src/core.c