Restructure and tidy

• add centralised configuration
  • allowing embedding through importing
  • easier to understand and pass through settings
• add extraMiddleware and extraHandlers
  • makes it more extendable
• update build to use ko instead of Kaniko+Dockerfile
  • build for more architectures (linux/amd64, linux/arm, linux/arm64, linux/s390x, linux/ppc64le)
• tidy up docs

Fixes: #5 (closed) Fixes: #6 (closed)