docs(guide): change prototype methods to scope methods in DI examples

As explained in 'Understanding the Controller Component', Controllers
written for new (post 1.0 RC) versions of Angular need to add methods to
the scope directly, not the function's prototype. Correcting this
example should remove any ambiguity, especially for beginners.
docs(cookbook): change prototype methods to scope methods in Buzz

As explained in 'Understanding the Controller Component', Controllers
written for new (post 1.0 RC) versions of Angular need to add methods to
the scope directly, not the function's prototype. Correcting this
example should remove any ambiguity, especially for beginners.