Add Support For OSX

[adamisntdead]

This covers the following changes:

• I updated the README to be a bit more clear, and remove the untested on mac
• I changed the build script to remove glob (reduce dependencies) and remove gomp. gomp causes a fair amount of trouble on OSX and the tests still all pass without it.
• I also just added the get_width function as I needed it, that also has docs and a test.

You should also consider adding something like travis ci for build integration, as that could test the whole thing, and add a documentation build script, which is needed as docs.rs cannot make the documentation due to its build script not having the quantum.h header.

Thanks for your work, and if you don't want to maintain this, I would be happy to

[adamisntdead]

Any update on this?