This is an old and unmaintained book. For an updated hackpack go here: https://github.com/BooleanCube/hackpack
This is a book written by BooleanCube for Competitive Programming!
The wiki folder gives you access to the book online itself on github. However, I recommend you just download the HTML version of the book since it is more legible and a bit more appealing to the eyes and has easier file navigation. The HTML folder is the folder named CPBook and the online version to view on github is called "Wiki".