Finish chapter "Integration of Athens in Spec"

[koendehondt]

• [ ] Use Alexandrie?
• [x] Check all code examples and images

[koendehondt]

@Ducasse

In P13, the example code AthensHello new openInWindow fails, similar to https://github.com/pharo-project/pharo/issues/16241. In P13 it works.

Would it be possible to backport the changes that make it work in P13? Otherwise, we cannot use the example.

Note that this is a reason to use P13, although elsewhere I have suggested not to do that. In fact, this is a bug in P12 that should be fixed.

[koendehondt]

@Ducasse In the first section there is a reference to Balloon Canvas. What is that?

[Ducasse]

BallonCanvas is the default canvas (not cairo) vai a Cplugging of Pharo and we can remove this reference.