Port updated example from rust-lang/rust

This commits ports one small part of rust-lang/rust#91861.  The main
change that PR made to `binary_heap.rs` was to replace vectors with
arrays in the examples.  We do *not* port such changes as they require
Rust 1.56.0, which is greater than this crate's current MSRV.  However,
it also simplified the setup in the example of `BinaryHeap::append()`,
and we repeat that here only with vectors instead of arrays.

Author: clint-white

src/binary_heap.rs

@@ -1064,11 +1064,8 @@ impl<T, C: Compare<T>> BinaryHeap<T, C> {
     /// ```
     /// use binary_heap_plus::BinaryHeap;
     ///
-    /// let v = vec![-10, 1, 2, 3, 3];
-    /// let mut a = BinaryHeap::from(v);
-    ///
-    /// let v = vec![-20, 5, 43];
-    /// let mut b = BinaryHeap::from(v);
+    /// let mut a = BinaryHeap::from(vec![-10, 1, 2, 3, 3]);
+    /// let mut b = BinaryHeap::from(vec![-20, 5, 43]);
     ///
     /// a.append(&mut b);
     ///