title: Assign a literal to an std::u16string or to an std::u32string
body: <p>As I know I may assign to a string a literal value as:</p>
  
  <pre><code>std::string s="good";
  std::wstring s=L"good";
  </code></pre>
  
  <p>how do I assign to a </p>
  
  <pre><code>std::u16string s= 
  std::u32string s= 
  </code></pre>