Reads an API's description into a WardrikRest.Spec.

A source is {module, opts}: a module with this behaviour, and what it reads. WardrikRest.Discovery reads Google Discovery documents. Write one for another format to load its APIs the same way:

defmodule MyApp.Described do
  @behaviour WardrikRest.Reader

  @impl true
  def read(opts), do: {:ok, %WardrikRest.Spec{...}}
end

WardrikRest.API.load({MyApp.Described, path: "priv/api.json"}, name: "my_api", ...)

The spec's schemas are JSON Schema, and refer to its types as %{"$ref" => name}; each tool's schema is fitted from them. See WardrikRest.Spec.