release version 2.0.0

[peterldowns]

• Implement mDNS for .local domains.
• removed daemon subcommand
• code cleanups
  • remove macOS app
  • better naming and organization
  • switch to buildGoModule, stop using gomod2nix
  • pin go1.20 in nix build because github.com/quic-go/quic-go cannot be built with go1.21
  • use caching in nix CI recipes
• Resolve some user-reported issues
  • Update secure/insecure domain docs (#17)
  • Explain "localias is already running" error message (#18)