Add std::to_string

README.md

@@ -352,6 +352,7 @@ s1 == "hello world"       // Comparison, also <, >, !=, etc.
 s1[0];                    // 'h' 
 s1.substr(m, n);          // Substring of size n starting at s1[m] 
 s1.c_str();               // Convert to const char* 
+s1 = to_string(12.05);    // Converts number to string
 getline(cin, s);          // Read line ending in '\n' 
 ~~~~