Added 3 examples for the box layout recipe:
1) Simple box layout demonstrating how to set actor properties
2) Trivial menu implementation using box layout
3) Demonstration app which enables tweaking and testing
of layout property interactions
Also inlined example 1 in the solution section and added
more explanatory text in the discussion.
The recipe covers how to use ClutterBindConstraint
to bind actor sizes together.
It gives some examples of where this approach is appropriate,
as well as explaining an alternative using allocation-changed
or notify::* signals.
Three examples are given:
1. Resizing a texture to the stage.
2. Resizing a rectangle to act as a transparent overlay on
top of a texture (using constraints).
3. Resizing a rectangle to act as a transparent overlay on
top of a texture, but with a size proportional to the texture
(using a handler connected to allocation-changed signals
emitted by the texture).
