Correct rustdoc warnings.

Part of #241.

src/unit.rs

@@ -3,8 +3,8 @@
 /// the `FromStr` implementation. Using this macro will create submodules for the underlying storage
 /// types that are enabled (e.g. `mod f32`). `@...` match arms are considered private.
 ///
-/// When using the pre-built [SI](si) system included with `uom` this macro allows for new units to
-/// quickly be defined without requiring a release. [Pull requests](pr) to add new units upstream
+/// When using the pre-built [SI][si] system included with `uom` this macro allows for new units to
+/// quickly be defined without requiring a release. [Pull requests][pr] to add new units upstream
 /// area always greatly appreciated.
 ///
 /// * `$system`: Path to the module where the [`system!`](macro.system.html) macro was run (e.g.
@@ -97,9 +97,7 @@
 /// ```
 ///
 /// [si]: http://jcgm.bipm.org/vim/en/1.16.html
-/// [quantity]: http://jcgm.bipm.org/vim/en/1.1.html
 /// [measurement]: http://jcgm.bipm.org/vim/en/1.9.html
-/// [kind]: https://jcgm.bipm.org/vim/en/1.2.html
 /// [pr]: https://github.com/iliekturtles/uom/pulls
 #[macro_export]
 macro_rules! unit {