Fix sys() bug; mov fxns from termcrate to utils

Add:
	src/utils.c
		-to contain utility functions (e.g. abs, addActor), so as to
		avoid cluttering up src/termcrate.c

	makefile
		-compilation statement for src/utils.c

Ref:
	src/termcrate.c
		-move certain fxns from src/termcrate.c to src/utils.c

Fix:
	src/audio.c
		-fix newly inserted conditional (which checks return value of
		system() call, mostly to amend compiler warnings), which
		expected the wrong return value on failure, and was registering
		a "success" as reason to exit(1).