KBFR API - version (level) 0
-------int 15-8FF4------------
Called with:
AX= 8FF4
BX= 1 (identifies the KB TSR)

Returns: If  KBFR is resident it will return:
AX= 0100 (AH is TSR id, AL=API level)
BX: resident's memory segment, >= 0050h.
Other regs, including Flags : unchanged

If BX were not 1 on call, KBFR would chain the request.

If no resident implementing the API is present,
int 15 will probably return with AH=86h, Cy set.
------------------------------

Design Notes:

This extremely simple API is nonetheless future-
aware. Of interest is the API version or level returned
in AL (currently 0). This "level" is independent of
individual executable versions. The intent is to
facilitate interactions between mismatched-versions
Transients and Residents.

A Transient WILL manage (unload/tweak) a same-API-level
Resident. It CAN manage a lesser-level Resident (if
the implementer bothers). It WON'T manage a higher-level
Resident (it may report mismatch to the user though).

API levels will not change often, quite possibly never will!

Current API level 0 depends on the Transient's awareness
of a few params "hard-coded" in the Residents; resident
code was reorganised to help keep these params unchanged
in the predictable future - even if the particulars of
the driver are changed (to implement other national keyboards,
for instance).

