Consider making unit interfaces more flexable than just `someUnitScale: Long`

[kevincianfarini]

These should probably expose functions of some sort so that unit which aren't perfectly divisible by a certain scale can still be somewhat accommodated.

[sargunv]

Example of such a real world unit, the US survey foot is (was) defined as 1200/3937 meters, which is ~304800609.6012192nm. It's not divisible by nanometers, so it can't currently be represented by this library.