Capitalisation and coding standards corrections

I promise to contribute something of more value in the future, but I've been using _s for reference purposes yesterday and today and there are a few very minor things grating on me.

I've corrected some inconsistencies in capitalisation in the comments. Obviously "correct" is subjective, but for example we have "Header" capitalised mid-sentence in the `header.php` comments, but not "footer" in `footer.php`.

In `single.php` we have "Template" capitalised mid-sentence.

Assuming we go lower case in general, I've tried to tidy this up a little bit so that any other ghastly pedants such as myself can rest easy.

I've also corrected a couple of very minor coding standards issues which I discovered along the way.