[c++/en] Clearly focus to C++11

Right now many C++ tutorial chapters use C++11 features and usually requirement for C++11 is mentioned (for nullptr and member variable initialization it's missing). I think C++ tutorial should clearly focus to C++11 and discourage using practices which can be better implemented with C++11 features.

Maybe there should be a simple list of features of C++11 compared to earlier versions and also mention of possible requirement of a compiler flag -std=c++0x/-std=c++11.