On *nix:
    perl -pi -e 's{\b((?:[a-zA-Z0-9]+_)+[a-zA-Z0-9])+\(\)\b}{<a href="$1.html">$1()</a>}g' *


   On Windows (I think):
    perl -pi -e "s{\b((?:[a-zA-Z0-9]+_)+[a-zA-Z0-9]+\(\)\b}{<a href=\"$1.html\">$1()</a>}g" *