vh calculations for regions were off by a factor of 100.

See Bug #25636
Merge pull request #64 from silviapfeiffer/vh-fixes

vh calculations for regions were off by a factor of 100.
Add some more hyperlinks to definitions and other specs.

DOM references:
* Document
* DocumentFragment
* ownerDocument
* ProcessingInstruction
* Text
* IndexSizeError

HTML spec references:
* HTMLElement
* addCue()

Local references:
* VTTCue
* VTTRegion