LOOP_CROSSFADE for audio loops

[SanyaWaffles]

viewtopic.php?f=7&t=71072

viewtopic.php?f=7&t=71036

Based on discussions, there was some discussion about adding some crossfade metadata for OGG/FLACs to help facilitate better looping in some cases.

Use case: where music doesn't sound good given the current vanilla looping. Alot more synth-driven ambient stuff tends to have difficulty looping, given the amount of noise generated, and changing the music would kill the vibe of the music track.