subscriber: fix broken docs links (#1825)

Apparently the links to the `Default::default()` methods didn't actually
work! Or, maybe they did work, but they don't on the latest nightly?

Regardless, this fixes them (as well as the RustDoc errors).

Signed-off-by: Eliza Weisman <[email protected]>

tracing-subscriber/src/fmt/mod.rs

@@ -223,7 +223,7 @@
 //! .with_thread_names(true) // include the name of the current thread
 //! .compact(); // use the `Compact` formatting style.
 //!
-//! // Create a `fmt` collector that uses our custom event format, and set it
+//! // Create a `fmt` subscriber that uses our custom event format, and set it
 //! // as the default.
 //! tracing_subscriber::fmt()
 //! .event_format(format)
@@ -420,7 +420,7 @@ pub struct SubscriberBuilder<
 /// ```
 ///
 /// [formatting subscriber]: Subscriber
-/// [`SubscriberBuilder::default()`]: SubscriberBuilder::default()
+/// [`SubscriberBuilder::default()`]: struct.SubscriberBuilder.html#method.default
 /// [`init`]: SubscriberBuilder::init()
 /// [`try_init`]: SubscriberBuilder::try_init()
 /// [`finish`]: SubscriberBuilder::finish()
@@ -432,10 +432,11 @@ pub fn fmt() -> SubscriberBuilder {
 /// Returns a new [formatting layer] that can be [composed] with other layers to
 /// construct a [`Subscriber`].
 ///
-/// This is a shorthand for the equivalent [`Layer::default`] function.
+/// This is a shorthand for the equivalent [`Layer::default()`] function.
 ///
 /// [formatting layer]: Layer
 /// [composed]: crate::layer
+/// [`Layer::default()`]: struct.Layer.html#method.default
 #[cfg_attr(docsrs, doc(cfg(all(feature = "fmt", feature = "std"))))]
 pub fn layer<S>() -> Layer<S> {
  Layer::default()