Reads the next meaningful token.

def NextToken(self):
    """Reads the next meaningful token."""
    self._previous_line = self._line
    self._previous_column = self._column

    self._column += len(self.token)
    self._SkipWhitespace()

    if not self._more_lines:
      self.token = ''
      return

    match = self._TOKEN.match(self._current_line, self._column)
    if not match and not self._skip_comments:
      match = self._COMMENT.match(self._current_line, self._column)
    if match:
      token = match.group(0)
      self.token = token
    else:
      self.token = self._current_line[self._column]