Find and implement method to convert non-mp3 files to mp3.

[mgermaine93]

Certain files in my library are of non-mp3 type (.m4a, etc). As a user, I want to account for this by converting all non-mp3 files to mp3.

• [x] Find method/module to convert non-mp3 files to mp3.
• [x] Implement it (in a test file or otherwise).
• [x] Test it and document it here.

[mgermaine93]

Pydub's AudioSegment seemed to fix this. The file is mp3 now and plays well: https://stackoverflow.com/questions/38110384/convert-any-audio-file-to-mp3-with-python