Add functional MDL parsing.

Add:
	src/graphics/matrix.(c, h)
		-Add `CLEAR()` macro and `copyMatrix()`.
		-Expose `Matrix_t` to public scope.

	src/interpreter/interpreter.c
		-Complete the first iteration of `evaluateMDLScript()`; the function
		correctly evaluates the `robot.mdl` file.

Mod:
	src/interpreter/stack/stack.c
		-Remove `Point_t` struct.
		-Make the initial item on a `Stack_t` an identity matrix instead of a
		`Point_t` -- the original, incorrect implementation was due to my
		misunderstanding of the purpose of the origin stack.