INT 21 - DOS 2+ - TERMINATE AND STAY RESIDENT                                   
	AH = 31h
	AL = return code
	DX = number of paragraphs to keep resident
Return: never
Notes:	the value in DX only affects the memory block containing the PSPsee Program Segment Prefix;
	  additional memory allocated via AH=48h is not affected
	the minimum number of paragraphs which will remain resident is 11h
	  for DOS 2.x and 06h for DOS 3.0+
	most TSRs can save some memory by releasing their environment block
	  before terminating (see #01378 at AH=26h,AH=49h)
	any open files remain open, so one should close any files which will
	  not be used before going resident; to access a file which is left
	  open from the TSR(Terminate and Stay Resident) A program which remains in memory after terminating in order to provide services to other programs or the user.  The name comes from the name of the DOS function call used to remain in memory after termination., one must switch PSPsee Program Segment Prefix segments first (see AH=50h)
SeeAlso: AH=00h,AH=4Ch,AH=4Dh,INT 20,INT 22,INT 27