The FLAC parser looks for the 'audio/flac' mime type, but Fedora
defines 'audio/x-flac' in /etc/mime.types for FLAC files. Add this mime
type to the audio parser.

Fixes #36.

Signed-off-by: Antoine Tenart <antoine.tenart@ack.tf>

- the `src` folder is now `libmat2`
- the `main.py` script is now `mat2.py`

- Normalize the case
- Strip \00, \r, space and \n
- Flatten metadata lists
- Add tests for audio files