Style Guide revision 2 (#142)

* Style Guide revision 2

Fixes #112.

I shied away from extending the `errors` bit because the changes are large enough as is, and I'd prefer to keep #118 for another revision later.

* Update style-guide.md

* Address Shane's feedback

* Reviewers feedback

* Update style-guide.md

* Update style-guide.md

Author: zbraniecki