Math roadblock

The D3DX library is deprecated, and the code is running into a LOT of
redefinitions of macros and other potential problems. That scares me,
but really all we're using the D3DX library for is basic linear algebra.
I'm going to swap out the D3DX uses with some custom math functions.
They're trivial to write, so it shouldn't take too long.
Work done, work to go

The math library is still messy, but the project builds. I'll fix up the
math library as needed, and I know there are a few functions I still
need to add, but it'll work for now.