* Add copy-to-clipboard button and JS
* Ignore line numbers if present
* Rewrite heading permalink code to use vanilla JS
* README: Add credits to zenorocha/clipboard.js (MIT License)
@iBug really wants a place here in the Credits section :P
* Add .no-copy for hiding the button, update docs
* Add td.rouge-code to selectors
* Fix navigator.clipboard branch
* Add screenreader text for copy button
* Restore focus to the button after copying
* Add site-wide enable switch