NAME
        DDoFmt -- format data into a character stream.

   SYNOPSIS
        DDoFmt(FormatString, DataStream, PutChProc, PutChData);
              A0            A1          A2         A3

   FUNCTION
        perform "C"-language-like formatting of a data stream,
        outputting the result a character at a time

   INPUTS
        formatstring - a "c"-language-like null terminated format
                string, with the following supported % types:
        DataStream - a stream of data that is interpreted according to
                the format string.
        PutChProc - the procedure to call with each character to be
                output, called as:
            PutChProc(Char,  PutChData);
                      D0-0:8 A3
                the procedure is called with a null Char at the end of
                the format string.
        PutChData - an address register that passes thru to PutChProc.