Clean engine.c, add drawCircle() macro.

Add:
	src/engine.c
		-remove textMatrix() and testRasterizeLine(), as the functions were used
		simply to test functionality and are no longer necessary.

	src/graphics.(c, h)
		-replace drawPolygon() body with the more efficient algorithm used by
		drawCircle() (which essentially renders a polygon with a large number of
		sides); replace drawCircle() with a macro that calls drawPolygon() with
		a number of sides equal to its radius, which is large enough to create
		the illusion of perfect circularity.