[WIP] Deal with raw utf8 data as well as strings, add TextDecoder for node via submodule (#43).

I've tried playing with TextDecoder here.  It works for single-byte strings, but fails with multi-byte.  Node doesn't have TextDecoder and TextEncoder natively, so I've also added that (you'll need to do `git submodule update --init --recursive` to pull it in) and attach them to the global for our tests, such that vtt.js can just rely on it being there.

I'm doing something wrong here, but it gets the plumbing in place at least.