[LANDAU][MECANIQUE] First three chapters

What's Changed

• Add first part of chapter 3 exercices by @SMajerowicz in #12
• Feat chap3 exercices by @SMajerowicz in #13
• Feat chap3 exercices by @SMajerowicz in #14
• Feat chap3 exercices by @SMajerowicz in #17

Full Changelog: 1.0.1...1.0.3