Various code improvements (#777)

* Remove deprecated use of std::u16::MAX
* Use `FromStr` for fallible `&str` conversions
* DRY up strings into constants
* Change `as_ref().map()` into `as_deref()`
* Use `Duration` for time constants and functions
* Optimize `Vec` with response times
* Move comments for `rustdoc` to parse

playback/src/audio_backend/pipe.rs

@@ -34,3 +34,7 @@ impl SinkAsBytes for StdoutSink {
         Ok(())
     }
 }
+
+impl StdoutSink {
+    pub const NAME: &'static str = "pipe";
+}