LIB-55: Allow using device numbers on Windows.

@jonnyjd: Made a new PR against master. A wrong drive number will now lead to an error instead of falling back to `MB_DEFAULT_DEVICE`.

This PR replaces https://github.com/phw/libdiscid/pull/1

EDIT by JonnyJD:
tracked in http://tickets.musicbrainz.org/browse/LIB-55