[FR] APE tag support in MP3, for parsing mp3gain's replaygain tags saved there

[nift4]

still need to figure out whether its really worth it see https://en.wikipedia.org/wiki/APE_tag and https://wiki.hydrogenaudio.org/index.php?title=APEv2_specification and https://wiki.hydrogenaudio.org/index.php?title=APEv1_specification and https://wiki.hydrogenaudio.org/index.php?title=APEv1 and https://wiki.hydrogenaudio.org/index.php?title=ReplayGain#MP3Gain