Add failing spec for SourceParser

Including a one for #862 and also other two.
Add passing SourceParser specs for preparation of refactor
Redesign parsing logic of cop disabling comment

Introduce more rubust logic that uses comment and token object from
Parser rather than parsing each source line with regexp.

This fixes #862.
Fix style issues by an oversight in the old comment parsing logic

The old parsing logic confused string literals including a cop disabling
comment such as 'something # rubocop:disable all' with real comments.
Merge pull request #867 from yujinakayama/redesign-comment-parsing

Redesign parsing logic of cop disabling comment