Add further unit_tests, helper macros, test/ CSVs.

Add:
	src/unit_tests.c
		-add SAVE, ASSERT_EQUAL, and enhanced TEST macros to aid in creating new
		unit tests and implementing existing ones by minimizing monotonous,
		repetitive code.
		-add numerous test*() functions, which test the functionality of
		virtually all functions contained in src/matrix.c (some, like
		freeMatrix(), can't quite be tested without a third-party tool -- for
		instance, a memory-checker).

	test/
		-add various CSV files used by src/unit_tests.c.