docstring documentation for python-bindings

[IshaanDesai]

Closes #3

[BenjaminRodenberg]

I think we do not need the doxygen_config file.

Additionally, it is important that we show how the datastructures in the python interface work. There are some important differences to the C++ API (e.g. pointers vs. numpy arrays) that should be reflected in the docstrings.

[BenjaminRodenberg]

I would suggest to stick to the numpy style docstrings (see here), if there are no reasons speaking against this.

Unfortunately, this seems to include a lot of manual work, since most python linters seem to have problems with cython code (I tried to use pylint with precice.pyx and you are just getting too many syntax errors).

[BenjaminRodenberg]

I found one typo. Rest looks absolutely great 👍