response_tokenizer: rewrite

This commit contains a rewrite of the response tokenizer, which
introduces lazy parsing of the response, handling of binary data, some
tests, as well as just generally more robustness against errors.

src/commands/queue/add.rs

@@ -15,6 +15,12 @@ pub struct AddRequest {
     position: Option<SongPosition>,
 }
 
+impl AddRequest {
+    pub fn new(uri: Uri, position: Option<SongPosition>) -> Self {
+        Self { uri, position }
+    }
+}
+
 impl Command for Add {
     type Request = AddRequest;
     type Response = ();