Regarding the [code](https://github.com/NCAS-CMS/cfunits/blob/0bd0e4dfda69b0f81ea998b5ea5edeceee5e6495/cfunits/units.py#L2213-L2215): It is only checked for signed integer. Are unsigned integers not possible? Similar to #32 I could add the code for unsigned integers. What do you think?
