Initial WebVTT contribution to the CG

Fellow WebVTT friends,

Attached is a starting point for our WebVTT specification.

It is an extract from the WHATWG's WebApps specification document.
Since the text was written by Google's Ian Hickson, and published on
the WHATWG site with a copyright attributed to Apple, Opera, and
Mozilla, the actual copyright ownership and hence grant to the CG
might be unclear to some. To clear up any confusion, and start on a
clean basis, all four companies are co-contributing the document. They
are cc'd here to make this clear.

The document was created by going through the WHATWG's WebApps
specification and extracting sections that are relevant to the WebVTT
specification that we are planning to create. Links to each of the
relevant chapters have been included so as to make it easier for the
editor to locate these sections and include them in the new
to-be-created WebVTT specification.

We can now also get started on writing a WebVTT tutorial and on
discussing suggested changes for WebVTT in this forum.

Best regards,
Silvia.