docs: Write The Fucking Manual

[dbartolini]

• [x] Move "Building" from README.md to "Hackers" section in the manual
• [x] Add License section
• [x] Integrate rtd theme
• [x] Features
• [x] Glossary
• [ ] Importing assets
• [ ] Sprite pixels-to-meter clarifications
• [ ] Lua Script Component
• [ ] Lua temporaries
• [ ] Explain main.lua and core/game/boot.lua relationship
• [ ] Mention Component instances cannot be cached
• [ ] Physics
• [ ] Introduction to DOD
• [ ] Lua: mention Crown uses LuaJIT and that it is fast: https://luajit.org/performance.html