P950NW: Add support for chainprinting (save tapefeed and tape)

[jab4]

Hi all and @boxine,
First, thanks for your software. I did some reverse engineering myself and hacked a text-only script in PHP.

Now the need arose to print raster graphics and I'm happy I found rasterprynt.

In __init__.py, I tried to hack chainprinting support myself to no avail, probably overlooked something.

   # yield b'\x1biC\x06\x1biM\x00'  # Various Mode settings: no auto cut
   # yield b'\x1bid\x00\x00'  # Margin = 0
     yield b'\x1biC\x05'  # Chainprint <<<< probably some bad sequence or overridden by later ESC sequence

Above semi-commented code prints with margin=0 and auto cut anyways.

What works for me in PHP is this snippet (0x1b==Esc, 0x69==i, 0x43==C) at the start:

            $seq.= "\x1b\x69\x61\x00"; # set command mode esc ia{command_mode}
            $seq.= "\x1b\x69\x43". bindec(implode('', [
                    0, # Bit 7: not used
                    0, # Bit 6: not used
                    0, # Bit 5: not used
                    0, # Bit 4: not used
                    0, # Bit 3: Special tape
                    1, # Bit 2: Chain printing
                    0, # Bit 1: Half cut
                    1, # Bit 0: Full cut
                ])); # set label cut settings (Esc i C)
            $seq.= "\x1b\x69\x6c\x00\x00"; # set label length: 0==auto
            $seq.= "\x1b\x24\x00\x00"; # set horiz position: 0

Any help how to make this work in rasterprynt would be highly appreciated.