📝🩹 Fix documentation on read the docs

[hf-krechan]

On read the docs we got the following error message:

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/ahbicht/envs/latest/lib/python3.7/site-packages/sphinx/registry.py", line 429, in load_extension
    mod = import_module(extname)
  File "/home/docs/checkouts/readthedocs.org/user_builds/ahbicht/envs/latest/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 965, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'sphinxcontrib.apidoc'

The motivation for the mentioned module is, that Sphinx reads the docstrings and generates automatically rst files from it.
This current setup works fine on our machines, but not on read the docs.
Luckily we are not the only ones with this issue: readthedocs/readthedocs.org#1139

So I used the same setup like the mozilla people: openwpm/OpenWPM#900

Additionally I added the folder of the generated rst-files to gitignore and fixed a docstring in one function.
In the future we have to be careful to indent multiline docstrings.