Return macro or block name from the current line.

def _compile(cls, lines):
        '''Return macro or block name from the current line.'''
        m = cls.RE_PASTE.match(lines.current)
        if m is None:
            raise MacroBlockUsageError(
                'Incorrect macro or block usage at line {}, {}\nShould be '
                'something like: #my_macro'.format(lines.pos, lines.current))
        return m.group(1)