Arnitech controller: the TOD set at boot, and a jump table at $FF00

A new option, ARNITECH_CONTROLLER, on in the mc64 configuration only.
IOINIT starts timer A with CIA #1's TOD on 50 Hz, the mc64's mains, and
if the Arnitech controller's signature "ARNI" is at $DE80, latches its
clock and copies its real time into the TOD, hours first and tenths
last, flipping bit 7 of an hour of 12 first, since the CIA flips it
back when 12 is written. Without the signature the TOD is left alone.

The Arnitech jump table at $FF00: "ARNI", version $01, two entries, and
JMPs from $FF06: $FF06 finds the first Card slot holding a Card of the
type in A (carry clear, the slot in A, its Card window's low byte in
X; carry set if none or no controller), $FF09 sets the TOD as IOINIT
does. $FF48-$FF80 stay clear. The code is in new files under
src/kernal/arnitech; other configurations build as before.

CONFIG.md

@@ -289,6 +289,12 @@ On the most widespread CPUs the D flag is not cleared upon entering interrupts.
 
 Feature needs 2 bytes in KERNAL segmment (for CPUs needing the patch), but at the same time allows optimizations allowing to gain some more bytes. If unsure - enable.
 
+### `ARNITECH_CONTROLLER`
+
+For the mc64 computers of arnitech only, whose expansion port holds the Arnitech controller at `$DE80`. IOINIT puts CIA #1's TOD on 50 Hz and, if the controller's signature `"ARNI"` is at `$DE80`, sets the TOD from the controller's clock. The Arnitech jump table at `$FF00` (`src/kernal/arnitech/ff00.arnitech_jumptable.s`) wraps the controller's registers.
+
+Feature needs about 120 bytes in KERNAL segment, and the page at `$FF00`. Disable on any other machine.
+
 ## Eye candy
 
 ### `COLORS_BRAND`