Fix broken links and use consistently absolute URLs

Except when files are in the same folder, let's use absolute paths when
linking to another chapter of the documentation.
Make references' index page consistent with the others

In order to be consistent with other index pages, let's rely on a list
to display the different available chapters.

Also add a missing link to the "Compatibility Index" chapter.
Use a table instead of a code block

This seems more adequate for users and consistent with the rest of the
document.