Update 2018-07-20

[theo-armour]

@launchandlearn/coaches

📣 Updates

• Added more themes. Now possible to add a custom-tailored theme
• Code cleanup.
• Finished adding Markdowm headers to all Markdown chapters

Also updates to: dev notes

Thinking about next stages

• Adding free open source images from Unsplash to the beginning of every chapter and wherever relevant
• Adding links to Wikipedia articles wherever relevant