WYSIWYG Markdown editor

[jstone-uw]

There are some decent in-place WYSIWYG editors for Markdown text. If we replace our editor, goals should include:

• Allow WYSIWYG editing with common keyboard shortcuts for formatting, and perhaps a lightweight formatting toolbar.
• Allow pasting formatted text. (Not all formatting will be preserved by Markdown.)
• Allow the user to edit raw Markdown too.