Link to W3C API spec added
Main added with Constructor.

* constructor takes sound source and Options
* Options === Settings, I just chose a different name
* `opt || new Opt` is to make it easier: to test and for browsers
* code verified with online JSLint (vide header)

Questions:
* default options - to be decided
* would be nice to plug in tests
* do we use strict? if it's a partially tutorial project - I guess so?)