Get XMS Version Number (Function 00h)

        ARGS:   AH = 00h
        RETS:   AX = XMS version number
                BX = Driver internal revision number
                DX = 0001h if the HMA exists, 0000h otherwise
        ERRS:   None

This function returns with AX equal to a 16-bit BCD number representing
the revision of the DOS Extended Memory Specification which the driver
implements (e.g. AX=0235h would mean that the driver implemented XMS
version 2.35). BX is set equal to the driver's internal revision number
mainly for debugging purposes.  DX indicates the existence of the HMA
(not its availability) and is intended mainly for installation programs.

NOTE: This document defines version 3.00 of the specification.