Set axis formatter based on dimension formatter.

def _set_axis_formatter(self, axis, dim, formatter):
        """
        Set axis formatter based on dimension formatter.
        """
        if isinstance(dim, list): dim = dim[0]
        if formatter is not None:
            pass
        elif dim.value_format:
            formatter = dim.value_format
        elif dim.type in dim.type_formatters:
            formatter = dim.type_formatters[dim.type]
        if formatter:
            axis.set_major_formatter(wrap_formatter(formatter))