Illustrate the Valuer and Scanner interfaces

[xaprb]

I think a page illustrating them would be a huge benefit. We (VividCortex) recently implemented a type that does seamless encrypt/decrypt and our code is absolutely clean. What a great thing. Jason Moiron's article on these is excellent. I think I would like to adapt it, trim it down, and give him credit: http://jmoiron.net/blog/built-in-interfaces/