Refactor build system to make configuration switching easier

[mwpenny]

What is the enhancement?

The Makefile is very coupled to the (libultra-based) Modern SDK. This issue tracks the work of refactoring it so it is easier to switch the toolchain and SDK at build time. There is also an opportunity to fix dependencies.

This will simplify the work of supporting other SDKs (and even potentially other platforms). CMake could be worth using here.

[mwpenny]

The game is now built using CMake.

This was quite a large undertaking, and I took it as an opportunity to make the build more modular and less error prone (proper dependencies between files, automatic build tool discovery, etc.). It will be much easier to add conditional logic around different build configurations now -- and just easier to use in general.