Rewrote ID3Manager, replaced EyeD3 with Mutagen.

ID3Manager is now called MetadataManager. Getter and setter methods with
immediate persistence have been replaced with properties and a separate
save() method.

Integration into indexer and models is not yet done and will follow with
the next commit.
shiva-indexer with docopt

Conflicts:
	indexer.py
	setup.py
Added docopt to requirements.pip
Rewrote indexer to use new MetadataManager
Better verbose logging
Convert audio length to an int
Replaced ACCEPTED_FORMATS with VALID_FILE_EXTENSIONS in indexer (refs #30)
Renamed count to track_count in indexer.py
Date parsing using dateutil
Improved argument handling in indexer
Return None as default year, not empty string
Added --reindex option to indexer
Fixed issue with release year parsing
MIXED CHANGES. REBASE.
Moved indexer
Slugifying artists and albums

In order to avoid repeated slugs in the database, we keep track of the artists
and albums we have indexed, slugified, and reuse them.
Added confirmation when dropping DB
Better output