Follow-up @foolip's suggestion in #81: 'firing' and other literatures. (

#83)

* Followed @foolip's suggestion in #81:

- Made a section for the explicit definition of what
'To fire a dataavailable event' means and referring to it.
- Linking 'fire' keyword to DOMSpec's concept-event-fire
- Cleaned up references to 'state' and the enumeration entries,
and reflowed some sequential entries into lists.
- 'To fire an error event' now uses a 'DOMException named e'
and the `ErrorEvent` has now a `DOMException` attribute.
- General reflow caused by adding href's

Also, removed MediaRecorder.css, unneeded