Investigate CodeMirror editor's live Markdown formatting

[ziz]

Prose uses CodeMirror to provide live Markdown syntax formatting (resized headers and so forth), which is kind of neat. Possibly it would be neat and not inconvenient to do so here too, and possibly Ace can style things that way.

Another possibility is that CodeMirror would make a better / easier / more entertaining editor for Capsule versus Ace.