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
Merge pull request #65 from silviapfeiffer/add-terms

Add some more hyperlinks to definitions and other specs.
Nitpick references
Merge pull request #67 from foolip/nitpick-refs

Nitpick references
Make the "Step 5" note part of the step itself to keep it in sync
Fix two markup errors
Merge pull request #71 from foolip/validation

Fix two markup errors
Merge pull request #68 from foolip/note-5

Make the "Step 5" note part of the step itself to keep it in sync
Remove empty title="" attributes

These were needed by Anolis, but have no effect for ReSpec.

To make the diff readable, no effort was made to re-balance the lines,
which makes it look a litte silly in places.
Remove some stray whitespaces, e.g. in "regionAnchor X"
Merge pull request #70 from foolip/rm-empty-title-attr

Remove empty title="" attributes
Merge pull request #72 from foolip/rm-stray-whitespace

Remove some stray whitespaces, e.g. in "regionAnchor X"
Fix the description of automatic line position

The algorithm that follows uses showing tracks, not active cues.
Merge pull request #74 from foolip/auto-line-position

Fix the description of automatic line position
Fix typo "where" -> "were"
Merge pull request #73 from foolip/typo-where

Fix typo "where" -> "were"
Unescape &gt; in --> (a majority of instances were not escaped)
Fix the name of a variable 'hours'
Fix some cross-references to DOM and HTML
Merge pull request #75 from foolip/unescape-gt

Unescape &gt; in --> (a majority of instances were not escaped)