docs(guide/controller): use `.controller` syntax

Use the recommended `module.controller` syntax rather than global
functions to define controllers in the examples.
docs(guide/controller): improve guidance and examples

Remove mention of global controller functions
Convert larger examples to runnable demos
Remove mention of pre-1.0 controllers, in particular discussion of
controller inheritance.

TODO: Probably could do with updating to explain the "controller as" syntax
at some point.

Closes: #4373