Command-line tool for writing a print-composer to file?

Question

I'm looking for a command-line tool, to write a previously generated print-composer to an image-file. The following resources I already saw:

• Related questions (1, 2)
• A gist

Nevertheless, all them are not doing, what I'm intending. I'm looking for a tool which looks like

qgisPrintComposer --print-composer 'my-composer1' --output image.png project.qgs

A starting point is here.