Rollup merge of rust-lang#78412 - camelid:cleanup-hash-docs, r=jonas-schievink

Improve formatting of hash collections docs

Author: JohnTitor

library/std/src/collections/hash/map.rs

@@ -606,7 +606,7 @@ where
     }
 
     /// Tries to reserve capacity for at least `additional` more elements to be inserted
-    /// in the given `HashMap<K,V>`. The collection may reserve more space to avoid
+    /// in the given `HashMap<K, V>`. The collection may reserve more space to avoid
     /// frequent reallocations.
     ///
     /// # Errors
@@ -619,6 +619,7 @@ where
     /// ```
     /// #![feature(try_reserve)]
     /// use std::collections::HashMap;
+    ///
     /// let mut map: HashMap<&str, isize> = HashMap::new();
     /// map.try_reserve(10).expect("why is the test harness OOMing on 10 bytes?");
     /// ```
@@ -898,14 +899,14 @@ where
 
     /// Retains only the elements specified by the predicate.
     ///
-    /// In other words, remove all pairs `(k, v)` such that `f(&k,&mut v)` returns `false`.
+    /// In other words, remove all pairs `(k, v)` such that `f(&k, &mut v)` returns `false`.
     ///
     /// # Examples
     ///
     /// ```
     /// use std::collections::HashMap;
     ///
-    /// let mut map: HashMap<i32, i32> = (0..8).map(|x|(x, x*10)).collect();
+    /// let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x*10)).collect();
     /// map.retain(|&k, _| k % 2 == 0);
     /// assert_eq!(map.len(), 4);
     /// ```

library/std/src/collections/hash/set.rs

@@ -412,7 +412,7 @@ where
     }
 
     /// Tries to reserve capacity for at least `additional` more elements to be inserted
-    /// in the given `HashSet<K,V>`. The collection may reserve more space to avoid
+    /// in the given `HashSet<K, V>`. The collection may reserve more space to avoid
     /// frequent reallocations.
     ///
     /// # Errors
@@ -918,7 +918,7 @@ where
     /// ```
     /// use std::collections::HashSet;
     ///
-    /// let xs = [1,2,3,4,5,6];
+    /// let xs = [1, 2, 3, 4, 5, 6];
     /// let mut set: HashSet<i32> = xs.iter().cloned().collect();
     /// set.retain(|&k| k % 2 == 0);
     /// assert_eq!(set.len(), 3);