methods required for Quantity API #13

For a possible Quantity API, am I correct in thinking that you've only used:

Quantity.init(value, unit)
Quantity.units
Quantity.magnitude
Quantity.m_as
Unit.pow
Unit.add
Unit.sub
Unit.mul
Unit.div

If it's just those methods, a Quantity API that would allow support for the array API seems very doable!