- Registered units of measure are now properties of PhysicalQuantity classes, and not individual instances of those classes.  As such, registering a new unit with a given PhysicalQuantity will make that unit immediately available to all inntances of that class.
   - PhysicalQuantity classes no longer define their units in their constructor, and instead have a new initialize() static method
   - The previously-existing registerUnitOfMeasure() method on physical quantity objects has been replaced with a new static addUnit() method
   - The HasSoUnitsTrait method addMissingSIPrefixedUnits is now static
- Added the toNativeUnit() method, to return values in their native unit of measure
- Added the isEquivalentQuantity() method, to support future situations where it's not obvious whether two physical quantities represent the same quantity type
- getSupportedUnits() is no longer available on physical quantities
- The PhysicalQuantity parent class is now named AbstractPhysicalQuantity
- Add a new DemonstrationTests test file, to demonstrate and test typical use cases
- All library exceptions extend from AbstractPhysicalQuantityException, making catching easier
- Added an interface for PhysicalQuantities, to support future work where not all physical quantity classes necessarily have the same parent