Merge remote branch 'elliot/cookbook-actors-composite'

Merge remote branch 'elliot/cookbook-actors-composite'

* elliot/cookbook-actors-composite:
  docs: Add reference to useful GObject tutorial
  docs: Explain why destroy() is implemented
  docs: Implement destroy() rather than dispose()
  docs: Don't use clutter_stage_get_default()
  docs: Change text on button
  docs: Add a note about other state variables
  docs: Complete composite actor recipe
  docs: Change order of functions in example to match docs
  docs: Add more comments on how allocate() works
  docs: Include code examples in the recipe
  docs: Explain enums for properties and signals
  docs: Don't set explicit size on button
  docs: Add example of preferred_height() and preferred_width()
  docs: Add recipe for creating a custom ClutterActor with composition
  docs: Add more comments on code example for composite actor
  docs: Improve example code formatting
  docs: Add some gtk-doc annotations to example
  docs: Add custom ClutterActor example which uses composition