Ae property does not return float

[runphilrun]

Nozzle property Ae is intended to multiply noz.At * noz.e and return a float as the property value.
Outside of the class, noz.At and noz.e return floats. Ae returns a method, which implies that it is not recognizing self.At or self.e as floats while computing the property.

[runphilrun]

When one property is set, the others do not auto-update.
Added an operation to update Ae, At, and e with respect to each other when one of these properties is set.