Code cleanup and JSHint fixes.
Rename assertion.
Add API option to not swap filenames.
Add API option to not swap selectors.
Make naive swapping of left/right default, to keep backwards compatibility.
Add script for running all tests.
Rename argument.
Fix bug related to default argument values.
Add tests for new command line arguments (ignore urls, ignore selectors), and refactor other tests.
Update docstrings.
Add command line options for ignoring urls and ignoring selectors.
Rename argument.
Add documentation for new command line options (ignore urls, and ignore selectors).
Increment version number, add changelog entry.