Add config files

[phipsgabler]

To get rid of too many flags, and allow for more customization of output, like advanced filtering, changing formats, internationalize strings, etc.

I'm thinking about using JSON, since we're already working with that, but I'm also open for other suggestions. And maybe before that the whole code should be refactored a bit.

Additionally, in the long run, we could also include the post-processing step, and call, eg., pandoc from Python, to get rid of the makefile, and replace it by this configuration.