Adding [embed] around URLs

After much research and wrangling, this is my attempt to improve the "modulize" TinyMCE button so that URLs contained within the module code behave in an oEmbed-friendly way like regular URLs.

It's far from perfect, but basically, if the selected text being wrapped in the embed container is nothing but a URL, it *also* gets wrapped in [embed] shortcodes in addition to the <aside> element.

I can explain how/why/etc in more detail on our call tomorrow.