Impliment some cool regex algos

[ethanpailes]

Previews seem sick, and also related in some respects what I've done with skip regex.

Apparently the egrep source is a good place to look for the kind of Aho-Corasick deep magic that regex optimization seems to be all about. I bet it works best for backtracking algorithms though.

Build one of these becuase who can say no to 20x faster than re2 using a DFA? I can't tell if this guy or previews is a better candidate to try to get upstreamed.