Get name from regular expression.

def regexNamer(regex, usePageUrl=False):
    """Get name from regular expression."""
    @classmethod
    def _namer(cls, imageUrl, pageUrl):
        """Get first regular expression group."""
        url = pageUrl if usePageUrl else imageUrl
        mo = regex.search(url)
        if mo:
            return mo.group(1)
    return _namer