Allow tuples to be passed to is_equivalent
Added note to changelog
Added a few negative assertions to test
Don't need to use an explicit list
Merge pull request #1521 from astrofrog/unit/is-equivalent-tuple

Feature request: have Unit.is_equivalent take tuples
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