Mitering in `expandPath`

[hkfb]

expandPath doesn't work well with sharp corners. Consider using mitering?

[markroland]

@hkfb I actually just read an article related to this at https://www.amygoodchild.com/blog/polygons-packing-expanding. I think it's more than I'm ready to take on in the near future, but yes I agree that it looks like there's a limit to what my code is supporting.