Rewrite the entire framework

[aalin]

This is the code from the rewrite that I started writing in August 2023.

Todo

• Implement a better VDOM
• Make the root layout work
• Fix string callbacks (onclick="event.preventDefault()")
• Generate image versions and static assets
• Reload routes when pages are added/removed
• mayu build to build apps
  • Make sure it includes everything
  • Cache assets during build time #32
  • Maybe generate a tarball with all the assets?
• mayu start to run built apps
• Prometheus endpoint
• Rewrite stack traces in Mayu::Modules::System by resolving modules
• Custom elements? #5

Issues that should have been fixed already in this branch

• Handle url() in CSS files #59
• Transform @foo to self.state[:foo] #58
• Transform CSS #9
• Validate nesting of DOM nodes #14