Go with GM styled comment requirement of `// fallthrough` syntax instead of curly braces.

* Apply some more of the styleguide to the STYLEGUIDE.md
* Clarify in notation that sometimes a `switch` may not always be the best option for readabilty in some cases.
* Leaving the choice of curly braces up to each contributor for the time being. Code folding is nice but ususally `switch` isn't that complex enough to need that.

Applies to #245 and #19