INT 2fH 4810H: Get Keyboard Input with Doskey Editing

                                                         Compatibility: 5.0+ 
 Expects: AX    4810H
          DS:DX address of special-format 128-byte buffer to hold input
 Returns: AX    status: 00H =success and...
                             DS:DX     buffer contains input text or
                             DS:DX[+1] contains 00H (means macro name was
                                      used; call again to expand the macro)
                       else =unsuccessful (bad input parms)
    Info: This fn performs two services:

          ■ Gets up to 126 bytes of text input from the keyboard (it can
            edit an existing line of text, too).

            It recognizes and handles all of the Doskey editing keys,
            including arrow keys, F8 to search the history list, etc.

          ■ Expands a Doskey macro to process parameters such as $1, or $*,

    DS:DX On entry, this points to a buffer formatted as a DkLineRec:

            Offset Size Contents
            ▀▀▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀
             +0      1  bBufMax     must be 80H
             +1      1  bTextLen    size of input text less the CR at end
             +2    126  abText      area to hold input text
                   128              size of a DkLineRec structure

          The bBufMax field must contain 80H.  The bTextLen must be the
          length of the current line of text (use 00H to input new text).
          For instance,

            db 80H,00H, 126 dup (0)

          On return, bTextLen will contain the length of the input, not
          including a CR (ASCII 0dH) which is appended to the end.  And
          abText will contain the characters of the input text.

          If, the user started the line with the name of a Doskey macro.
          then this fn set bTextLen to 00h.  In that case, you should
          immediately call this fn again to obtain the expanded text of the
          macro.  In that case, this fn displays the expanded text and
          places its size in bTextLen and the text itself in abText.

   Notes: ■ Doskey does not initially display abText.  When using this fn
            to edit an existing line of text (i.e., when bTextLen is non-
            zero on entry), you may want to use DOS fn 09H or 40H to
            display the text before calling.

          ■ There appears to be no way to differentiate between the case
            where the user typed Enter only and the case where the user
            typed a macro name.

          ■ All Doskey keystrokes are supported, including those that
            handle command-line history (such as up arrow to see
            previously-typed commands).  When the user inputs text, that
            line is added to the command-line history.  If you expect to
            process macros, you must always call this fn again when the
            bTextLen comes back containing 00H.

          ■ Be sure to use INT 2fH 4800H to verify that Doskey is loaded
            before using this fn.

See Also: INT 2fH 48xxH (Doskey Functions)
          INT 2fH: Multiplex Interrupt
          DOS Functions