[Protocol] Implement generic response with dyn (#56)

* Implement generic response as enum

* First draft of implementing into_common()

* Make common response type generic

* Use macros and generics to reduce repetition

* [Games] Add dynamically dispatched CommonResponse trait

This adds two traits: "CommonResponse", and "CommonPlayer", when the
generic game query function returns a response it returns a pointer to
its original response type that implements "CommonResponse".

Both common traits require that "as_original()" be implemented, this
returns an enum containing a pointer to the original type.

Both traits have a concrete method "as_json()" that returns a struct
containing data fetched from all of its methods as. This struct
implements serde and can hence be serialized as required.

The traits require a few other methods be implemented, those being the
fields that are common across all types. All other methods have a
default None implementation so that each response type only needs to
implement methods for fields that it has.

* [Game] Implement common traits for JCMP2 response

* [Fmt] Run cargo fmt

* Fix doctest failing

* Run cargo fmt

examples/generic.rs

@@ -1,15 +1,17 @@
-use gamedig::{protocols::GenericResponse, query, GDResult, GAMES};
+use gamedig::{protocols::types::CommonResponse, query, GDResult, GAMES};
 
 use std::net::IpAddr;
 
-fn generic_query(game_name: &str, addr: &IpAddr, port: Option<u16>) -> GDResult<GenericResponse> {
+fn generic_query(game_name: &str, addr: &IpAddr, port: Option<u16>) -> GDResult<Box<dyn CommonResponse>> {
     let game = GAMES.get(game_name).expect("Game doesn't exist");
 
-    println!("Querying {:#?} with game {:#?}.", addr, game.name);
+    println!("Querying {:#?} with game {:#?}.", addr, game);
 
     let response = query(game, addr, port)?;
+    println!("Response: {:#?}", response.as_json());
 
-    println!("{:#?}", response);
+    let common = response.as_original();
+    println!("Common response: {:#?}", common);
 
     Ok(response)
 }