Cache rewrite, syntax highlighting, inline assets, bugfixes

• Revamps caching logic. 🙌 , @afischer and @shawn620!
• Adds syntax highlighting for code blocks. 🙌 , @smores !
• Inlines styles for error pages. 🙌 , @chrisfrank!
• Adds a new environment variable to support https offloading. 🙌 , @salexpdx!
• Build in support for youtube embeds. 🙌 , @shawn620!