Overload addPoint(), remove addTransformPoint().

Add:
	src/matrix.(c, h)
		-add overloaded `addPoint()`, which allows an optional `w` coordinate
		argument, with the help of some macro hacking (fundamentally identical
		to the mechanism used by `src/screen.h:drawPixel()`).

Rem:
	src/(matrix.(c, h), unit_tests.c)
		-remove `addTransformPoint()` declaration, definition, and substitute
		any calls to it with (the newly overloaded) `addPoint()`.