Add missing "basic usage" sections to docs, fix review comments.

Author: nathankleyn

src/libcollections/btree/map.rs

@@ -347,10 +347,15 @@ impl<K: Ord, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///
-    /// let mut map: BTreeMap<&str, isize> = BTreeMap::new();
+    /// let mut map = BTreeMap::new();
+    ///
+    /// // entries can now be inserted into the empty map
+    /// a.insert(1, "a");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new() -> BTreeMap<K, V> {
@@ -364,6 +369,8 @@ impl<K: Ord, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///
@@ -385,6 +392,8 @@ impl<K: Ord, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///
@@ -408,6 +417,8 @@ impl<K: Ord, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///
@@ -428,6 +439,8 @@ impl<K: Ord, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///
@@ -460,6 +473,8 @@ impl<K: Ord, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///
@@ -490,6 +505,8 @@ impl<K: Ord, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///
@@ -519,6 +536,8 @@ impl<K: Ord, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// #![feature(btree_range, collections_bound)]
     ///
@@ -592,6 +611,8 @@ impl<K: Ord, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// #![feature(btree_range, collections_bound)]
     ///
@@ -667,6 +688,8 @@ impl<K: Ord, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///
@@ -1275,6 +1298,8 @@ impl<K, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///
@@ -1305,6 +1330,8 @@ impl<K, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///
@@ -1338,6 +1365,8 @@ impl<K, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///
@@ -1357,6 +1386,8 @@ impl<K, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///
@@ -1376,6 +1407,8 @@ impl<K, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///
@@ -1393,6 +1426,8 @@ impl<K, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
+    /// Basic usage:
+    ///
     /// ```
     /// use std::collections::BTreeMap;
     ///