Cleanup permalink generation

Fix permalink generation to not contain various smells. See verbose description in the last commit in this PR.
@dkubb I tested only the ones where mutant does not emit mutations for. We do not have a mutation from `<` to `<=` as we have the inverse from `<=` to `<` to follow the 'semantic reduction principle' (`<` includes less than `<=`).

I'm actually thinking we should emit the inverse also since it'll be easy to kill. The author should be 100% sure about `<` vs `<=` so it should prove to mutant he is 100% aware about his choice. Your thoughts?