Add doctests for iter_mut and into_iter of BTreeMap.

Add spacing as dictated by standard rust code style.

src/libcollections/btree/map.rs

@@ -1058,6 +1058,24 @@ impl<K, V> BTreeMap<K, V> {
     }
 
     /// Gets a mutable iterator over the entries of the map.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::BTreeMap;
+    ///
+    /// let mut map = BTreeMap::new();
+    /// map.insert("a", 1u);
+    /// map.insert("b", 2u);
+    /// map.insert("c", 3u);
+    ///
+    /// // add 10 to the value if the key isn't "a"
+    /// for (key, value) in map.iter_mut() {
+    ///     if key != &"a" {
+    ///         *value += 10;
+    ///     }
+    /// }
+    /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
     pub fn iter_mut<'a>(&'a mut self) -> MutEntries<'a, K, V> {
         let len = self.len();
@@ -1072,6 +1090,21 @@ impl<K, V> BTreeMap<K, V> {
     }
 
     /// Gets an owning iterator over the entries of the map.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::BTreeMap;
+    ///
+    /// let mut map = BTreeMap::new();
+    /// map.insert(1u, "a");
+    /// map.insert(2u, "b");
+    /// map.insert(3u, "c");
+    ///
+    /// for (key, value) in map.into_iter() {
+    ///     println!("{}: {}", key, value);
+    /// }
+    /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
     pub fn into_iter(self) -> MoveEntries<K, V> {
         let len = self.len();