generalize genius artist matching to use slug()
generalize genius artist matching to use slug()

shamangeorge/beets,beetbox/beets,ibmibmibm/beets,beetbox/beets,jackwilsdon/beets,shamangeorge/beets,beetbox/beets,sampsyo/beets,beetbox/beets,sampsyo/beets,sampsyo/beets,sampsyo/beets,ibmibmibm/beets,ibmibmibm/beets,shamangeorge/beets,ibmibmibm/beets,jackwilsdon/beets,shamangeorge/beets,jackwilsdon/beets,jackwilsdon/beets