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);
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            the procedure is called with a null Char at the end of
            the format string.
    PutChData - an address register that passes thru to PutChProc.