returning None.
Changed priority of converters: they are tried in *reversed* order
of registration.
Added 'MoneyConverter' ('quantity.money.converter.py').
0.8.1 Refactored class 'Term'.
Some bug fixes.
0.8.0 Exceptions raised by Quantity.__new__ changed to QuantityError.
Added function 'generateUnits'.
Added sub-package 'money'.
0.7.3 Added function 'sum'.
Added method 'Quantity.allocate'.