Fixes #121 -- ASSERT_TRUE( isHorizonal() )

- Also WEBVTT_INVALID_CUESETTING rather than
  WEBVTT_INVALID_CUESETTING_DELIMITER, which is deprecated
Fixes #121 - Corrected comment typo and wording
Fix incorrect comment and rewrap.

There's no point saying what line the assert will error on in
the comment; it's clear enough in the actual assert and too hard
to maintain the information in two places.
Merge pull request #3 from rillian/issue-121

Issue 121
Merge pull request #121 from caitp/issue-121

CueSettingVertical.BadDelimiter assertion makes no sense