human-readable errors in read() and write()
merge
changelog thanks for discogs plugin (#283 / #210)
only IOErrors are IOErrors
discogs: tweak colorization & installation docs

I thought having "MusicBrainz" colored green was a little distracting since
it's the common case (and universal without the discogs plugin), so this just
makes it neutral-color in that case.
discogs: expand docs ever so slightly
don't penalize Discogs matches for lacking MBIDs

This removes the distance component for MBIDs for matches that don't have
MBIDs. (Previously, when importing an album that already has MBIDs, Discogs
would be unfairly penalized.)