More general wrapping

[kokes]

There is basic wrapping implemented in https://github.com/kokes/nbviewer.js/commit/1aa90456b239de2ef0e599f34363ac6556d460b4, but I'd like it to be extended to all pre elements - well, all but code inputs, which should overflow: scroll.

Also, make sure that the current CSS implementation is the most compatible one, there seems to be some contention about that.