code_styleguide: Filled out Javascript and some CSS

Looking back on my past pull requests, I found that a lot of comments were about my code style. (Shoutout to y'all for keeping a rigid codebase!) So, I went through my old PRs and transcribed your comments into the empty style guide. Maybe now we'll have less line comments that say "Semicolon" :+1: 

Fixes #85.