Fix formatting in documentation

Removed trailing whitespaces and extra newlines. Added some missing
punctuation. Replaced unicode characters that aren't commonly used
with the more common character.

The replaced unicode characters are
- ’ (U+2019) to ' (U+0027)
- “ (U+201C) to " (U+0022)
- ” (U+201D) to " (U+0022)

docs/theming.md

@@ -193,5 +193,3 @@ These colors represent intent, and so are not often changed, but you can do so i
 - `--neutral` - Neutral color, usually grey / `#272f4d`
 - `--white` - Just white / `#fff`
 - `--black` - Just black / `#000`
-
-