Add styles for tutorial section and prism.js for syntax highlighting

Add minified highlighting for JS
Add styles as SCSS partial and tweak to taste
Add prism via script tag - couldn't work out how to add it with Require
to ensure global Prism variable is availble and plugin runs correctly
Add classes to HTML for prism
Add styles and colors for tutorial section
Add tutorial section to nav and remove "Who?" because it's really the footer
Fix color of "contribute on github" with a specificity boost