chore: Add deny(broken_intra_doc_links) to all crates (#616)

tonic/src/lib.rs

@@ -68,6 +68,7 @@
     rust_2018_idioms,
     unreachable_pub
 )]
+#![deny(broken_intra_doc_links)]
 #![doc(
     html_logo_url = "https://raw.githubusercontent.com/tokio-rs/website/master/public/img/icons/tonic.svg"
 )]

tonic/src/macros.rs

@@ -67,6 +67,8 @@ macro_rules! include_proto {
 ///     pub(crate) const FILE_DESCRIPTOR_SET: &[u8] = include_bytes!("/relative/protobuf/directory/descriptor_name.bin");
 /// }
 /// ```
+///
+/// [`OUT_DIR`]: https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-build-scripts
 #[macro_export]
 macro_rules! include_file_descriptor_set {
     ($package: tt) => {