Chapter 22 and chapter 23

[Cinderella-Man]

Two new chapters added:

• Chapter 22 - 80/20 win with pure logic
In the 20th chapter, we refactored most of the code inside the Naive strategy, promising ourselves that it would make
testing and maintenance easy. In this chapter, we will test that, proving that we are now able to test the vast majority of
the system using trivial, easy-to-understand input-output tests.
• Chapter 23 - Back to the Monolith
In this chapter, we will look back at the issues/complexity umbrella applications cause. We will port the whole application
to a new Phoenix skeleton, using this opportunity to refactor/merge logic that was previously spread across multiple
apps.

Additionally, issues from the PR #36 were resolved