Support for chords when using Sequence, use nested arrays to use chords

[arjuna-dev]

1. Please make all pull requests on the dev branch.
2. Don't commit build files
3. Try to get all tests to pass.

[tambien]

Thanks for the CL, but i think this would break the Sequence syntax. What i've done in the past for making sequences of chords was to use chord symbols (e.g. ["C", "Am", "Dm", "G"]) and then define a Map which maps the chord name to the array of notes