Document some macros.

Author: emilio

src/extra_assertions.rs

@@ -1,6 +1,8 @@
 //! Macros for defining extra assertions that should only be checked in testing
 //! and/or CI when the `testing_only_extra_assertions` feature is enabled.
 
+/// Simple macro that forwards to assert! when using
+/// testing_only_extra_assertions.
 #[macro_export]
 macro_rules! extra_assert {
     ( $cond:expr ) => {
@@ -15,6 +17,8 @@ macro_rules! extra_assert {
     };
 }
 
+/// Simple macro that forwards to assert_eq! when using
+/// testing_only_extra_assertions.
 #[macro_export]
 macro_rules! extra_assert_eq {
     ( $lhs:expr , $rhs:expr ) => {