Named types for type level operators (error improvement 2)

[sufferiing]

In the previous error improvement, the units system was changed to generate named classes for quantities that can be used interchangeably with the structural Quantity<> type. This PR allows type level quantity manipulations such as Multiplied<Q1, Q2>, Divided<Q1, Q2>, Exponentiated<Q, N> and Rooted<Q, N> to return the named classes (if possible) rather than the generic Quantity<> class.

It does this by generating a "compile time type function" from the corresponding Quantity<> class to it's named counterpart when the NEW_UNIT macro is invoked. Then with this function we can created a wrapper Named<Q> that will produce the named version of a quantity type if it exists.

For example this offending code:

previously generated this error:

with this change, it now generates this error:

[Aang099]

All looks good!