Added MP3 support and more

[ThePotatoGuy]

#1657

I think we're done with music after this.

This adds MP3 and OPUS support to the music menu.
This also adds tag support so that the music files are listed in [artist] - [title] format instead of filename.
In addition, OGG and OPUS files can be looped if they are provided with loopstart and loopend metadata tags, which specify the seconds to start and end the loop, accordingly.

MP3 files do not support loop tags atm

In depth looping instructions

1. open the audio file in audacity
2. Export as OGG / OPUS and edit metadata
3. Add a tag for loopstart to mark where to start loops of audio file (in seconds)
4. Add a tag for loopend to mark where to end loops of the audio file (in seconds)
5. put audio file in custom_bgm/ folder.

Additional changes

• The mutagen library has been added. It can read metadata tags, but I've stripped it so it only includes the ogg / opus/ and mp3 parts. The library is less than 1MB in size
• I've added the mplus 2p font so we can have songs with jpn glyphs show up appropriately. This font is free to use and is arguably the best font in existence.

Also here's a nice picture of the new font.

[williamjcm]

The normal format for the LOOP* tags is in samples, though.

I have many files using that format.

[ThePotatoGuy]

We opted to use seconds since its native to Renpy

But I think I'll move the lookup for those tags to custom MAS-related ones and do some math with the RPGMaker ones to get them to work.

Just hold on a bit.