book: Chapter 5 since markers (smart pointers)

Add 'since C++11' markers to shared_ptr/unique_ptr/weak_ptr. The RAII
intro already strongly motivates why smart pointers exist.

Author: changkun

book/en-us/05-pointers.md

@@ -26,6 +26,8 @@ These smart pointers include `std::shared_ptr`/`std::unique_ptr`/`std::weak_ptr`
 
 ## 5.2 `std::shared_ptr`
 
+*(since C++11)*
+
 `std::shared_ptr` is a smart pointer that records how many `shared_ptr` points to an object, eliminating to call `delete`, which automatically deletes the object when the reference count becomes zero.
 
 But not enough, because using `std::shared_ptr` still needs to be called with `new`, which makes the code a certain degree of asymmetry.
@@ -82,6 +84,8 @@ std::cout << "pointer3.use_count() = "
 
 ## 5.3 `std::unique_ptr`
 
+*(since C++11)*
+
 `std::unique_ptr` is an exclusive smart pointer that prohibits other smart pointers from sharing the same object by copy construction or copy assignment, thus avoiding errors due to repeated destruction or freeing:
 
 ```cpp
@@ -148,6 +152,8 @@ int main() {
 
 ## 5.4 `std::weak_ptr`
 
+*(since C++11)*
+
 If you think about `std::shared_ptr` carefully, you will still find that there is still a problem that resources cannot be released. Look at the following example:
 
 ```cpp

book/zh-cn/05-pointers.md

@@ -27,6 +27,8 @@ order: 5
 
 ## 5.2 `std::shared_ptr`
 
+*（C++11）*
+
 `std::shared_ptr` 是一种智能指针，它能够记录多少个 `shared_ptr` 共同指向一个对象，从而消除显式的调用
 `delete`，当引用计数变为零的时候就会将对象自动删除。
 
@@ -80,6 +82,8 @@ std::cout << "pointer3.use_count() = "
 
 ## 5.3 `std::unique_ptr`
 
+*（C++11）*
+
 `std::unique_ptr` 是一种独占的智能指针，它禁止其他智能指针经由拷贝构造或拷贝赋值的方式与其共享同一个对象，从而避免重复析构或释放带来的错误：
 
 ```cpp
@@ -139,6 +143,8 @@ int main() {
 
 ## 5.4 `std::weak_ptr`
 
+*（C++11）*
+
 如果你仔细思考 `std::shared_ptr` 就会发现依然存在着资源无法释放的问题。看下面这个例子：
 
 ```cpp