Add auto unit type selection?

[ChrisBarker-NOAA]

In pyNUCOS, we allow the user to convert some units without specifying a unit type:

us.convert("ft", "m", 1.0)

But if you want to convert to, say "fraction", and you may not know that unit)type is (e.g. Concentration, not length, or mass or ..) than there are issues, as "fraction" may belong to more than one unit type (by the NUCOS definition). note that this can be an issue with lots of units, like "oz" which could be a weight or a fluid oz.

In PyNUCOS, we do support this use case -- the "UnitType" is optional in the convert function. It's done by building a mapping with the FindUnitTypes() function in:

https://github.com/NOAA-ORR-ERD/PyNUCOS/blob/master/unit_conversion/unit_conversion.py

Note that it excludes certain unit types and specific units, to avoid clashes.