Keeping 50 items needs to use ltrim 0 49, not ltrim 0 50.

- Typo, wording in Lists and in Sets.
Add directory for french translation and only use Ubuntu fonts.
Chapter 0: About.
Chapter 0: Introduction.
Chapter 0: Getting started.
Chapter 1: The Basics.
Chapter 1: The building blocks.
Chapter 2: The data structures.
Chapter 2: Strings.
Chapter 2: Hashes.
Chapter 2: Lists.
Improved Makefile: PDF depends on its source and configuration file.
Chapter 2: Sets.