Add backface culling, code unclean.

Add:
	src/engine.c
		-add temporary test() function, to test backfaceCull().

	src/matrix.c
		-add backfaceCull(), to perform backface-culling on triangles.

Mod:
	src/matrix.c
		-in addSphere(), create spheres from half-circles rotated up to 360
		degrees instead of full circles rotated up to 180 degrees. Maps more
		nicely onto backface-culling, because all of the points are added with
		the correct (counterclockwise) winding; with full circles, half of the
		points would have been added in the incorrect order.
Clean up addPolygon() methods, add documentation.

Add:
	src/matrix.(c, h)
		-add addHalfPolygon() macro to complement addPolygonFull().

Rem:
	src/matrix.c
		-remove individual addPolygon() and addHalfPolygon() functions, in favor
		of an addPolygonFull(), which intakes an angle argument that can be
		tailored to create either half or full polygons as necessary.
Fix missing-dome sphere bug.

Fix:
	src/matrix.c
		-fix a bug where a pole of the sphere wasn't visible due to backface
		culling, caused by the fact that it was composed of single lines
		(triangles with two identical vertices), as opposed to full triangles.
Add test function for backface_culling submission.

Add:
	src/engine.c
		-add simple `test()` function to evince backface-culling functionality,
		for the backface_culling assignment submission.
Update unit-tests, add color to terminal output.

Add:
	src/unit_tests.c, test/*.csv
		-Update `testAddPolygons()`, `testAddSphere()`, and `testAddTorus()`
		unit tests to test against the results of the updated corresponding
		functions (which render each figure differently after the implementation
		of backface-culling, due to fixes to some bugs that became apparent).
		-Unit-tests do not yet account for which points are visible (ie,
		backface culling has no actual impact on them), testing only against the
		points present in a given matrix (before they're plotted on the screen).

	src/unit_tests.c
		-Add statements to print success/failure messages in color, if a given
		terminal supports them.

	src/engine.c
		-Remove now obsolete `test()`.