Add audio from FMA

[stellaywong]

Happy New Year mirdata maintainers!

I am preparing a mirdata loader. I was following the directions for the >5MB option but the FMA individual mp3 downloads require an API key, and the link to request it no longer works.

Two options for next steps are:

1. Ask the mirdata user to download FMA full to their local, which is 900GB.
2. Upload the FMAK subset to Zenodo. At ~25GB for 5400 songs, it seems this is still a lot of files.

Please let me know what you would recommend?