Remove effect of rtl / ltr on position related rendering for non-snap-to-lines.

It was an oversight to leave this in the rendering section - text position is
supposed to be calculated always from the left edge for horizontal cues or top
edge for vertical cues.
Merge pull request #102 from foolip/rtlPosition

Remove effect of rtl / ltr on position related rendering for non-snap-to-lines.
Improve on some of the wording.
Fix some typos.
Be consistent when referring to "text alignment".
Merge pull request #103 from foolip/positionTypos

A few preparatory changes to position related spec text.
Merge commit '778b966fd85caf39f88085a140f305b00d4c3c36' into revert-regions
Merge commit '28f3cb2a09fffd6bfbfa644d16755043759d7482' into revert-regions

Conflicts:
	webvtt.html