Add support to systems without file and fprintf

[Christer-Ekholm]

Support small embedded systems which does not like to import FILE support from libraries.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (82b51a3) 97.40% compared to head (953c9b0) 97.45%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #14      +/-   ##
==========================================
+ Coverage   97.40%   97.45%   +0.04%     
==========================================
  Files           1        1              
  Lines         154      157       +3     
==========================================
+ Hits          150      153       +3     
  Misses          4        4              

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[Christer-Ekholm]

And here example how my system printer callback looks like

int DLOG_vShellFPrintF(void * ctx, const char* format, ...)
{
    va_list args;
    va_start(args, format);
    char buffer[160];
    int len = vsnprintf(buffer, sizeof(buffer), format, args);
    va_end(args);

    if(len > 0)
    {
        uint32 sentBytes;
        HAL_UartSend(s_TerminalPort, (uint8*)buffer, len, &sentBytes);
    }
    return len;
}

[likle]

Hi @Christer-Ekholm ! That looks very cool, thank you for your contribution!