Only highlight note names within word boundaries.

I have a few note names which are very short and simple (things like 'pa'). As a result, I get a lot of improper highlighting in another notes. Any word containing 'pa' will become underlined.

I've tweaked the regex slightly to only highlight note names within word boundaries. If a note name is surrounded by any word boundary, it is highlighted. If it is embedded within other letters or numbers, it is not highlighted.

Perhaps a personal preference thing, so no worries if you opt to reject this.