Add new section on trait bounds.

exercises/04_traits/14_outro/src/lib.rs

@@ -0,0 +1,10 @@
+// TODO: Define a new `SaturatingU16` type.
+//   It should hold a `u16` value.
+//   It should provide conversions from `u16`, `u8`, `&u16` and `&u8`.
+//   It should support addition with a right-hand side of type
+//   SaturatingU16, u16, &u16, and &SaturatingU16. Addition should saturate at the
+//   maximum value for `u16`.
+//   It should be possible to compare it with another `SaturatingU16` or a `u16`.
+//   It should be possible to print its debug representation.
+//
+// Tests are located in the `tests` folder—pay attention to the visibility of your types and methods.