TTVal + TTML 2 Implementation Report

Good morning/evening,

I have checked in at [1] an initial pass at TTVal, a TTML 2 Validation
Processor implemented in JavaScript for the Node.js environment.

[1] https://github.com/sandflow/ttval

The objective is to cover the TTML 2 tests at [2] for use in the
implementation report.

[2] https://github.com/w3c/ttml2-tests/blob/master/validation/tests.json

Attached is the current feature coverage.

Best,

-- Pierre