[Repronim-trd3] result_renderer

[Christian Haselgrove]

> not yet
>
> this whole setup was inherited from datalad, where a few do use it.
> would make sense to use it in your case, where diff itself would return
> a structure for rendering.  This way I believe if used in Python we
> would get the structure while on cmdline - the rendering

Okay, thanks.  What I'm actually after is the ability to specify the
exit value from a command-line interface.

Please see:

    https://github.com/ReproNim/niceman/pull/339

Let's not make this a bikeshed -- we can make this better later if
needed, but I've pulled it out so we can agree on a concept.  I need
something working that I can use in the diff interface.

c