Update cue2json.

I've added functionality so that cue2json can print JSON to a file with
the same name as the vtt passed or walk the a dir tree and rewrite JSON
files that it finds have a matching vtt file.
Move JSON files over to new format with region data.
Add region tests to test the region keyword and delimiter.
Change region percent settings to be stored as ints by default.

The spec says to interpret these as integers.
Update README for new JSON file format and cue2json code.