Closes #1133

The list is getting out of hand. Which is great, actually, but the front-page
shouldn't be dominated by it.

2 doesn't have getBoundingClientRect, which we use extensively.

Closes #1062

They no longer work (as part of twitters continuing quest to
make itself obsolete).

So that I don't have to say 'no' so often

As shown at GOTO Aarhus this month

Closes #843

This was especially noticeable with non-default font-sizes. The wrapper div and additional pre are required due to using the font-size provided by the browser (using em throughout).

Closes #768

Closes #764

(codemirror2 -> codemirror)