General design
Before diving into the code, let's understand the high level idea.
A help system is a tree, where each node represent a page of the help, that the user can visualize.
Each page is linked to several child pages. Depending on the choice of the user, the next page is displayed to him.
In this example, the user start from Page 1, and depending on his choice, he can go to Page 2 or Page 3.
To make this help system easier to naviguate, we want to add some path back to parents, so the user can as well choose to come back one step before.
We also add the idea of "root", so the user can come back to the beginning easily.
