Fix various typos

Hey. This project looks awesome!

One issue is [this line](https://github.com/doodzik/rubysierung/blob/0a9663880b26fdbe7f54270d6a6715812f978ee6/lib/rubysierung.rb#L38), which prevents using `rubysierung` in `irb` (or `pry` or `ruby -e` or any non-file context).

I am also based in Berlin. It might be fun to meet up in-person and hack on this. Let me know if that sounds interesting to you.