Extended Jan81 by kev to know about:

	11/40-style floating point instructions (fadd, fmul, etc.)
	11/45 stst flt.pt. instruction
	standalone instructions (halt, wait, reset, etc.)
	spl instructions (special case added so could check range)
	emt
	inter-space instructions (mfpi, mfpd, etc.)

Unfortunately, "wait" is also known to <sys.s> (the wait system call).
However, this should not cause any problems, as a standalone program will
not be making system calls (and thus should not be including <sys.s>),
while to a normal user-mode program, the wait instruction is very boring
(as it really does wait for the next interrupt!).

Some DEC-standard names are still not recognised (trap, absd, ldcdf, etc.)
due to their limited use (under unix) and symbol-table speed considerations.

BUG:
	10
.data
.=10^.			/ . is relative to TEXT segment, not DATA segment
	20		/ resulting in "ld" complaining about EOF on file

ANOTHER BUG:
	mov	(r5), fr0
	moves (r5) to r0, not fr0 - should flag an error at assemble time

To_do: should know about system calls - would have to introduce a new type
	to force it to follow sys call only - avoid "wait" problem above
