Traps and Zaps: Vienna Game (Légal's Mate)

Another chestnut from Chess Openings: Traps and Zaps.  1. e4 e5 2. Nc3 Nc6 3. f4 d6 4. Nf3 a6?! 5. Bc4 Bg4?! 6. fxe5 Nxe5?

White to play and win

And here's the answer!