Docs: Move to new intra-doc links, make events non-exhaustive. (#19)

Far cleaner and more reliable than the old doc-link pattern. Also allowed me to spot some event types and sources which should have been made non_exhaustive.

src/tracks/looping.rs

@@ -1,7 +1,7 @@
-#[derive(Copy, Clone, Debug, Eq, PartialEq)]
 /// Looping behaviour for a [`Track`].
 ///
 /// [`Track`]: struct.Track.html
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub enum LoopState {
     /// Track will loop endlessly until loop state is changed or
     /// manually stopped.
@@ -11,7 +11,7 @@ pub enum LoopState {
     ///
     /// `Finite(0)` is the `Default`, stopping the track once its [`Input`] ends.
     ///
-    /// [`Input`]: ../input/struct.Input.html
+    /// [`Input`]: crate::input::Input
     Finite(usize),
 }