setup.py missing install_requires entry for numpy

[dnwe]

something like

    install_requires=[
        'numpy>=1.8'
    ],

should be added (as appropriate), else a setup.py-based install won't work

[sustefil]

Actually it seems mutagen is also needed, this worked for me:

    install_requires=[
        'numpy',
        'mutagen',
    ]

now I can install successfully with pip3 install .