Next queued song (#123)

* Added code to fetch next queue item

* Updated README

* Give it a go

* Minor docker compose change

* Added docker-compose defaults

* Code refactor

* Removed data from being fetched

* Added test

* Formatting

src/callers/mod.rs

@@ -3,5 +3,6 @@ pub mod song;
 
 pub mod endpoints {
     pub const QUEUESONG: &str = "/api/v2/song/queue";
+    pub const NEXTQUEUESONG: &str = "/api/v2/song/queue/next";
     pub const QUEUEMETADATA: &str = "/api/v2/song/metadata/queue";
 }