It should be fairly easy: The do_spans() function in wakautils.pl contains the regexps that parse it. Look for "[\*_] or similar (meaning "match either a * or a _").
And some people use : : for emoting in text. You can't account for the idiosyncracies of every user - at some point you just have to ask them to conform. * * is an old and accepted way to place emphasis in unformatted text, while : : is not.
I furthermore maintain that emoting has no place in written text other than instant messaging, which is emulating a face-to-face discussion. Books do not contain emoting, and neither do letters. There are far more elegant ways to communicate the same thing, and using emoting just makes you look childish.