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.
I used to think that way, but I’ve decided to go with the Ruby standard and I am quite used to it now. Not having these empty lines means more visible lines of code on the screen, and from my personal experience, it’s not harder to read.

(It did take me a while to adjust to, though.)