A lot of changes, most basic things work now

Still need to implement things like sqrt() and add all of the composite
units. I should probably also add more unit types for testing purposes.
Also should probably test units with non integer powers more as I have
done almost no testing of non integer exponents.
Now can check if a unit is compatible with another

A unit is compatible if the type and power of every unit are the same
Now you actually can verify that units are compatible

The last commit had a bug where it didn't check the power