[dev] Build up unit tests and "native" platform

[kbhomes]

Flesh out unit tests by implementing them against the "native" platform, which simulates a PS2+ controller on the compiler's platform. It obviously can't communicate with a real console, but it should be able to simulate enough of the device to test it's logic.

Also, it may be worthwhile to create unit tests that can run on-device. This would help to determine that platform abstractions are functioning properly.