Adds in support for responsive margin helpers. Now you can suffix your margin classes with breakpoint language to allow your margins to change shape!
This is not thoroughly vetted, so if you try a complex combination, your results may vary.
Examples
.m1 will add a margin top and bottom of 1rem
.m2-ltsm will overwrite the margin to be top and bottom of 2rem when viewing smaller screens ("less than small")
.mr4-xs will overwrite the margin to be margin-right of 4rem on extra-small screens
etc.