RID is a short function that the echo context can be passed into, which returns the request ID as it grabs it from the response header.

WrapMiddleware creates a new handler by wrapping middleware around a final handler.

Handler is a function signature which retains most of the important bits of http.HandlerFunc, but enhances it with an incoming context, so we don't need to mangle the one in http.Request, and returns an error, which will be useful once we have an error handling middleware.

Middleware is a function signature that takes a Handler, and returns a Handler.