Remove leading/trailing '_!' from CODRA EDUs and unescape its double quotes.

def cleanup_codra_edus(self):
        """Remove leading/trailing '_!' from CODRA EDUs and unescape its double quotes."""
        for leafpos in self.tree.treepositions('leaves'):
            edu_str = self.tree[leafpos]

            edu_str = EDU_START_RE.sub("", edu_str)
            edu_str = TRIPLE_ESCAPE_RE.sub('"', edu_str)
            edu_str = EDU_END_RE.sub("", edu_str)

            self.tree[leafpos] = edu_str