* Add speed conversion function
* Add test for speed utility functions
* Update unit system tests
* Fix incorrect unit conversions in tests
* Fix some test errors
* Calculate speed units from smaller set of constants
* Fix typo in speed test
* Use pytest.approx for checking floating point values
* Change other instance of speeds needing to be pytest.approx
* Revert changes to unit system
* Fix oopsie in defining in/day and in/hr
* Parametrize test
* Add comments describing calculations & remove duplicate test
