Add serialize support for enums

src/codec/audio_service.rs

@@ -1,7 +1,10 @@
 use ffi::AVAudioServiceType::*;
 use ffi::*;
+#[cfg(feature = "serialize")]
+use serde::{Deserialize, Serialize};
 
 #[derive(Eq, PartialEq, Clone, Copy, Debug)]
+#[cfg_attr(feature = "serialize", derive(Serialize, Deserialize))]
 pub enum AudioService {
     Main,
     Effects,