Write a section/appendix with more information on exploitation

[g-kouv]

There is a TODO in the "exploitation primitives" section that reads:

The references in this section describe complicated modern exploits. Consider linking to simpler exploits,
as well as some tutorial-level material.

While reviewing #124, Kristof suggested adding a similar TODO that shows how we can start from a signed integer overflow and get to more powerful primitives.

Since exploitation isn't the main focus as the book, IMO this kind of material would work well as an appendix, rather than another section in the memory vulnerabilities chapter. It could include a few simple examples of vulnerabilities and how they can lead to problems, and include links to existing material about exploitation and secure coding.

The topics mentioned in #106 might also make sense as another appendix following this one, or combined into a single appendix.