Add copy-example-to-clipboard button

[morrisonlevi]

Copying to the clipboard can be done in modern browsers with JavaScript's document.execCommand('copy', ...) which will copy the current selection. I'm not sure the way to feature detect support.

Essentially when a user clicks the button we need to highlight the code snippet and then copy it.

[Wes1262]

That used to work only in designMode/contenteditable and only if browsers were set explicitly to allow so. But just recently I read that there is a new API somewhere that doesn't require adobe flash to copy to clipboard. Though, i think it's huge effort for a very little improvement (Ctrl+C or Context>Copy isn't hard work :D) but i'll check what we can do and if we can do it easily.

[morrisonlevi]

Proof of concept jsfiddle by iroegbu.

[philip]

Idea from the audience: I wonder about using https://clipboardjs.com/ as it's well-tested and small. I've used it in the past with great success.