Update live preview on keyup

Registering the event listener means that after every keypress in the
text entry field, the live preview will re-render.
Create stub for transdownify() function

This will be the function that handles the heavy-lifting for pattern
matching on input text
Changes "transcriptulate" to "transdownify"

Seems consistent with terminology used by other programmers including
Brett Terpstra:
http://brettterpstra.com/2012/06/20/marky-the-markdownifier-reintroducti
ons/

refs #1