INT 20 - Program Terminate

	CS = address of PSP

	returns nothing

	- INT 20 restores the terminate, Ctrl-Break, and critical error
	  exit addresses from values in the PSP, flushes all buffers, frees
	  memory and returns to DOS via the termination handler address
	- does not close FCBs
	- this function is no longer recommended, but can be used by
	  version of DOS before 2.0, see  INT 21,4C  and  INT 21,0