Define minimum api level required

        Entry:
          AX = DE0Bh
          BL = API level major version number
          BH = API level minor version number

        Return:
          AX = maximum API level (AL = major, AH = minor)

        Note:   If the requested API level is greater than the version of
                DESQview, a "You need a newer version" error window is
                popped up.