Allow input/interaction/output with Quantities (closes #751)
Remove print statements left-over from testing
Add test cases, resolve some problems that appeared
Add tests for time/quantity interaction
Also define __rtruediv__ so python3 works correctly
Add documentation for interaction of Time and TimeDelta with Quantity
Correct documentation for unresolvable links to Quantity
Rewrite of value validation with try/except to avoid python3 problem