Ensure both backend and client honors the content negotiation headers.

Use content negotiation for HTTP extender. TODO: need to genericise the content negotiation logic to apply possibly to other extenders.

Use example project to setup integration tests among the modules.

Split modules to each package.

Turn operation class into a builder.

Use Map instead of Set for easy referencing of endpoints and operations.

Add implementation for fetch method in tests.

Add basic recipe system for resources.

Allow basic functionality for HTTP servers.