Fix tests
Pull out the MP4 parser
Pull out id3v1 parsing
Add a generic place to register metadata parsers
Clean up metadata.js and stop using almost-global variables
Move metadata.js
Make the top-level metadata parser use Promises too!
Fix tests
Clean up id3v2 parser
Move test files to match the structure of the js/ dir. This way, tests are automatically rerun if the file they're testing is changed
Fix lint errors (some of these were real errors in edge cases too)
Bug 907929 - Part 1: Decode the image block from VorbisComment.
Bug 907929 - Part 2: Unit tests.