Contribution of test cases to WebVTT development

Dear WebVTT CG,

Attached please find a collection of test cases that were developed
for WebVTT and a html page that describes most of the attached vtt
files and what they are testing.

This can be added to a test suite at the CG/W3C under the CLA,
contributed by Google.

Best Regards,
Silvia Pfeiffer.