Add support for micromath

[Kaikallon]

Hello,

First off, I'm a beginner in Rust so I don't expect this PR to be accepted without modifications. Feedback is very welcome.

The reson for adding this support is that I wanted to use uom in an embedded environment without support for std. I need support for trigonometric functions, but I still want to keep the power of unit analysis. This is an attempt at doing that.

One concern that I have about my contribution is that I think that there is too much copy pasting. I have played around with this for a while and I wasn't able to find a different way that works.

[Kaikallon]

I see now that num-traits is an optional feature of micromath. I'm not sure how or if that should be used. Probably because I never understood the purpose of num-traits. Many traits for numeric operations are already defined in the core and standard library.

[Kaikallon]

Another thing that I noticed is that my implementation could be applied to ratio also. Further, there are more functions which could be implemented, such as sqrt()

[iliekturtles]

Thanks for the PR! Another possible solution for trig functions on no_std is in #309 and uses libm. I'll compare the two (I just need some patience, I'm well behind on PRs) and see what kind of overlap there is.

I also kicked off the tests, but it looks like there is some bitrot and the latest compiler is causing some errors unrelated to your changes.