Formatting change to Matrix::SetPerspective
Adding static ZeroVector to Vector4 class
Mouse/Scroll events now use DeviceMotion args (aka double)
Window callbacks send relative device motion.
They store previous positions in a cache, initially set to 0.
Comment additions
Comment addition to SimpleEngine.
Adding EngineAsEventHandler example.
GLFW window key callback now calls KeyEvent for handler
Flub with recent Window fix.