Clean up dependencies of librespot-core

* Use sub-crates of future
* Remove unnecessary pin-project
* Removed unused crates and features
* Replace futures channels by tokio channels
* Use serde's "derive" feature flag instead of serde_derive

core/src/apresolve.rs

@@ -9,6 +9,7 @@ cfg_if! {
         use std::error::Error;
 
         use hyper::{Body, Client, Method, Request, Uri};
+        use serde::{Serialize, Deserialize};
 
         use crate::proxytunnel::ProxyTunnel;