Updated Merge::AcceptedCorrectionsIntoContentAt:

* respect file_patterns in Rtfile so that we can apply a subset of files only
* all matching is limited to relevant_paragraphs for higher confidence and better accuracy
* made conditions for auto-merge more strict for higher confidence and to avoid multiple application of a single correction
* improved console reporting
* allow straight double quotes inside kramdown IALs
* refactored class for better testability
* allow subtitle_marks and gap_marks before paragraph numbers
* improved specs