Implement RegExp using XRegExp by Steven Levithan

@mbx This implementation of RegExp using XRegExp appears to support at least some of the PCRE extensions. And it will be extensible in ways that the native RegExp object isn't. And it compiles the expression you posted on IRC yesterday:

RegExp("^\\s*(?P<sign>-)?((?P<h>\\d+:)?(?P<m>\\d+:))?(?P
\\d+(\\.(?P<ss>\\d*))?)", "i")

Don't know if it actually works though.

Maybe we should give it a try. What do you think?