Refactor doc strings according to google specifications

[MaxDall]

          [Here](https://google.github.io/styleguide/pyguide.html#doc-function-args) it does state to only include typing specifications if the function is not type annotated already. But there is also no direct guide on how to format the additional annotation. Maybe it's just not the right document. But anyway, this should not be part of this PR.

Originally posted by @dobbersc in #331 (comment)