Interface tags

[Caellian]

I propose addition of a marker proc_macro:

#[interface(method = "GET", path = "/orgs/{org}/memberships/{username}", version="2022-11-28")]

Implementation of this proc_macro would simply pass-through input tokens, and generate a file ("OUT_DIR/interface/get/orgs.(org).memberships.(username)") that can then be used by CI to generate an always-updated list of implemented routes using github/rest-api-description, periodically.

This would allow exhaustive, and always up-to-date, API coverage testing.