Work on new differ.
Finish initial iteration of diff formatting.
Change some names.
Change order of classes.
Make more progress on diff code.
Make Comparer.compare_strings() work.
Refine the diff output.
Fix and skip some tests.
Stub out --check-template argument.
Start implementing check-template mode.
Create TemplateRenderer class.
Move Comparer class.
Stub out Comparer.compare_dirs().
Finish code path for --check-template (though not yet working).
Change log statements to debug.
Rename result to output.
Create ArgProcessor class.
Continue refactoring directory compare code.
Create DirDiffInfo class.
Update docstrings.