Add fpcalc.exe and discid.dll to ignore list

fpcalc and discid.dll are put in the development directories when you
build the development environment according to the instructions on the
musicbrainz web site - and they should not form part of the repo.
Handle Performer tags stored in ID3v2.3

Performer tags are stored as part of the IPLS tag in ID3v2.3 and this is
put into the TIPL tag when read by mutagen. This fix adds unknown TIPL
roles as Performer tags.