Update previous tips to reflect guaranteed copy elision in C++17

[Brian-M-J]

Many early tips talk about RVO, copy elision etc., but make no mention of C++17. As a result, they often say things like, "Strictly speaking the compiler is not required to perform copy elision".

Now that C++17 guarantees copy elision in certain situations, a note can be added to the tips similar to the one given for number 11. It can tell readers to refer to number 166.

These are the tips which I found mention copy elision and were made before C++17:

1. Number 11
2. Number 24
3. Number 77
4. Number 101
5. Number 117
6. Number 120