Docs: minor fixup - inserting API details

[Lucas-C]

Fix this:

Into this:

Note: if in the end the Doxygen + breathe setup does not bring up much added value,
in regards to the concerns expressed in #25 (comment),
feel free to get rid of it.
Maybe we can give it a few weeks / months to evaluate the benefit.
AMHA the Markdown-based Sphinx documentation is the most valuable part of the generated documentation.

[felixguendling]

Thank you! :)

Until now we didn't have the developer capacities to document everything and knowledge was shared within the office at Technical University of Darmstadt. Most of the code was written at times when everyone working on MOTIS worked in the same room. This changed now, so we have to adapt our approach on sharing knowledge. I think this is a good starting point. I also added a style guide to the main repo.