Merge pull request #176 from amab8901/patch-1

Functions `a` and `b` are unused. Silence the lint.

src/04_pinning/01_chapter.md

@@ -553,10 +553,12 @@ note: required by a bound in `std::pin::Pin::<&'a mut T>::get_mut`
 > #         this.b = self_ptr;
 > #     }
 > #
+> #     #[allow(unused)]
 > #     fn a<'a>(self: Pin<&'a Self>) -> &'a str {
 > #         &self.get_ref().a
 > #     }
 > #
+> #     #[allow(unused)]
 > #     fn b<'a>(self: Pin<&'a Self>) -> &'a String {
 > #         assert!(!self.b.is_null(), "Test::b called without Test::init being called first");
 > #         unsafe { &*(self.b) }