add support for parsing playlists as events + more

This brings several changes with it:

- `Mpv::get_property` now returns `Option`s in case `data` is
  nonexistent. There could be cases where this is different from
  `MpvDataType::Null` and `MpvDataType::MinusOne`.

- `MpvError` now implements `PartialEq`

tests/integration_tests/misc.rs

@@ -1,26 +1,30 @@
-use mpvipc::MpvExt;
+use mpvipc::{MpvError, MpvExt};
 
 use super::*;
 
 #[tokio::test]
 #[cfg(target_family = "unix")]
-async fn test_get_mpv_version() {
+async fn test_get_mpv_version() -> Result<(), MpvError> {
     let (mut proc, mpv) = spawn_headless_mpv().await.unwrap();
-    let version: String = mpv.get_property("mpv-version").await.unwrap();
+    let version: String = mpv.get_property("mpv-version").await?.unwrap();
     assert!(version.starts_with("mpv"));
 
     mpv.kill().await.unwrap();
     proc.kill().await.unwrap();
+
+    Ok(())
 }
 
 #[tokio::test]
 #[cfg(target_family = "unix")]
-async fn test_set_property() {
+async fn test_set_property() -> Result<(), MpvError> {
     let (mut proc, mpv) = spawn_headless_mpv().await.unwrap();
     mpv.set_property("pause", true).await.unwrap();
-    let paused: bool = mpv.get_property("pause").await.unwrap();
+    let paused: bool = mpv.get_property("pause").await?.unwrap();
     assert!(paused);
 
     mpv.kill().await.unwrap();
     proc.kill().await.unwrap();
+
+    Ok(())
 }