More style fixes

This is the second part of my crusade against non-standard code style; the first part being #476.

There are two reasons why these changes were not in #476:

1. Rubocop got updated with a lot of new checks, and this PR ensures we adhere to the guidelines set forth in that new Rubocop.

2. I got over the attachment to my personal preferences (such as TODO’s not being postfixed by a colon).

I will probably squash this PR into a single commit, since it gets quite noisy otherwise.
doesn't it make it code harder to read?