improve yt-dl error output

src/player/youtube.rs

@@ -52,11 +52,24 @@ pub fn youtube_dl(uri: &str) -> Result<Vec<Song>, String> {
         .output()
     {
         Ok(out) => out,
-        Err(_) => return Err("youtube-dl error".to_string()),
+        Err(why) => return Err(format!("youtube-dl error {:?}", why)),
     };
 
     if !out.status.success() {
-        return Err("shell error".to_string());
+        let stdout = match String::from_utf8(out.stdout) {
+            Ok(string) => string,
+            Err(_) => String::new(),
+        };
+
+        let stderr = match String::from_utf8(out.stderr) {
+            Ok(string) => string,
+            Err(_) => String::new(),
+        };
+
+        return Err(format!(
+            "Shell error\nstdout: {}\nstderr: {}",
+            stdout, stderr
+        ));
     }
 
     let files = check_result!(convert_output(&out));