[2.0] Documentation Refresh

[hmans]

• Update existing README to reflect new bits
• Provide a summary example at the top of the README
• Add links to codesandbox and stackblitz sandboxes with the demo game
• Describe/document the demos
• Document world.archetype
• Document without
• Document the where iterator generator
• Document generics of archetype, with, without and where
• Document typical pitfalls (like world.with("foo").without("bar") vs. world.without("bar").with("foo"))
• Add a "How It Works" section that explains buckets etc.
• Add a section on performance