Refactor to ReSpec

This (big) branch refactors the whole spec to use ReSpec, instead of not using anything, which will ease editing, and provide nice cross-references, handles normative and informative references, markup for WebIDL, and a bunch of other goodies.

It can be previewed at http://padenot.github.io/web-audio-api

This is simply a port, the content is the same, but it would be great if people could double check.

I agree that there could be more crossrefs and the like, this is merely a first step towards a spec that is nice to use. Adding more linkable content in a maintainable fashion will be way easier and can come after.