Adding Stockfish 5 recipe

Stockfish 5 is the strongest chess engine in the world. The latest release just won the TCEC tournament.
It's checking if the processor supports the `POPCNT` instruction. There's a description in my comment above, quoted here:

> The formula now checks Hardware::CPU to pick the right architecture, and for modern processors also verifies the existence of the POPCNT instruction (the use of which is a very significant performance increase important to chess engines).