Split the Parsing and Processing sections into seperate files

[RickEyre]

vtt.js is starting to get really big and a little hard to look at. I think it would be good to split the different major components into different files and the build step can take care of putting everything together.

This is similar to issue #200, but focuses on splitting up what's already in vtt.js rather then packaging things together in different ways that are already separate like vttcue.js, vttregion.js, etc.

[goatandsheep]

yes I agree. I need to just be able to parse the VTTCue to JSON and back