kijiproject.github.com: Express Music.  Update to reflect latest code.

Also add some additional explanations for things that I found confusing
when I read this the first time.

Attempt to bring consistency to `var` versus "var" (using the former
everywhere).
commit: https://github.com/kijiproject/kijiproject.github.com/commit/d29c228c60c09d3fe2403b90adf05cdb4b3e32fe