docs: address community issue feedback (#5 #338 #142 #246 #136 #303)

- const README: rewrite the space-saving claim per issue #5 follow-ups
  (constant-expression const vs #define immediates; which const qualify
  as constant expressions)
- const README: fix the class-section diagnosis per issue #338 (overload
  resolution picks the const overload; the restriction only surfaces
  once that overload is removed)
- sizeof README: virtual-inheritance result is compiler-dependent
  (GCC merges vbptr+vfptr -> 16, MSVC keeps them separate -> 32) #246
- static README: new section on internal linkage / access restriction
  with anonymous-namespace comparison #142
- 10-day practice: full problem list table + fixed day links #136
- new design_pattern/singleton/singleton_default.hpp: reusable
  thread-safe CRTP singleton template, compile+concurrency tested #303

cpp2.0/cpp11/README.md

@@ -1,8 +1,10 @@
-# C++新特性
+> 本文档由 [C++那些事网站](https://light-city.github.io/stories_things/modern-cpp/cpp11/cpp11/) 同步生成，网站版本含多语言与更新排版。
+
+# C++11 新特性概览
 
 ## 1.C++11新特性
 
-- [Variadic Templates](./variadic)
+- [Variadic Templates](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/variadic)
 
 - Spaces in Template Expressions
 
@@ -11,17 +13,17 @@
   vector<list<int>> // before c++ 11 error error: ‘>>’ should be ‘> >’ within a nested template argument list,c++11后可以正常通过
   ```
 
-- [nullptr and nullptr_t](./nullptr.cpp)
+- [nullptr and nullptr_t](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/nullptr.cpp)
 
-- [Automatic Type Deduction with auto](./auto.cpp)
+- [Automatic Type Deduction with auto](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/auto.cpp)
 
-- [Uniform Initialization ](./uniform_initialization.cpp)
+- [Uniform Initialization ](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/uniform_initialization.cpp)
 
-- [initializer_list](./initializer.cpp)
+- [initializer_list](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/initializer.cpp)
 
-- [explicit for ctors taking more than one argument](./explicit.cpp)
+- [explicit for ctors taking more than one argument](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/explicit.cpp)
 
-- [range-based for statement](./auto.cpp)
+- [range-based for statement](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/auto.cpp)
 
   ```cpp
   for(decl:col) {
@@ -29,33 +31,33 @@
   }
   ```
 
-- [=default,=delete](./default_delete.cpp)
+- [=default,=delete](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/default_delete.cpp)
 
   如果你自行定义了一个ctor,那么编译器就不会给你一个default ctor
   如果强制加上=default,就可以重新获得并使用default ctor.
 
 - Alias(化名)Template(template typedef)
 
-  - [alias.cpp](./alias.cpp) 
-  - [template_template.cpp](./template_template.cpp)
+  - [alias.cpp](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/alias.cpp) 
+  - [template_template.cpp](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/template_template.cpp)
 
-- [template template parameter](./template_template.cpp)
+- [template template parameter](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/template_template.cpp)
 
-- [type alias](./type_alias.cpp)
+- [type alias](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/type_alias.cpp)
 
-- [noexcept](./noexcept.cpp)
+- [noexcept](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/noexcept.cpp)
 
-- [override](./override.cpp)
+- [override](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/override.cpp)
 
-- [final](./final.cpp)
+- [final](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/final.cpp)
 
-- [decltype](./decltype.cpp)
+- [decltype](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/decltype.cpp)
 
-- [lambda](./lambda.cpp)
+- [lambda](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/lambda.cpp)
 
-- [Rvalue reference](./rvalue.cpp)
+- [Rvalue reference](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/rvalue.cpp)
 
-- [move aware class](./move.cpp)
+- [move aware class](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/move.cpp)
 
 - 容器-结构与分类
 
@@ -63,8 +65,8 @@
   - (2) 关联式容器包括：set/multiset,map/multimap
   - (3) 无序容器(C++2.0新引入,更换原先hash_xxx为unordered_xxx)包括：unordered_map/unordered_multimap,unordered_set/unordered_multiset
 
-- [Hash Function](./hash.cpp)
+- [Hash Function](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/hash.cpp)
 
-- [tuple](./tuple.cpp)
+- [tuple](https://github.com/Light-City/CPlusPlusThings/tree/master/cpp2.0/cpp11/tuple.cpp)
 
   学习资料：https://www.bilibili.com/video/av51863195?from=search&seid=3610634846288253061