when --debug print note name

src/tone.rs

@@ -82,6 +82,24 @@ impl Tone {
     pub fn i32(&self) -> i32 {
         self.0
     }
+
+    pub fn string(&self) -> String {
+        match self.i32() {
+            57|69 => "a",
+            58|70 => "a+",
+            59|71 => "b",
+            60|72 => "c",
+            61|73 => "c+",
+            62|74 => "d",
+            63|75 => "d+",
+            64|76 => "e",
+            65|77 => "f",
+            66|78 => "f+",
+            67|79 => "g",
+            68|80 => "g+",
+            _ => "?",
+        }.to_string()
+    }
 }
 
 #[cfg(test)]