todo before course

• remove chapter 0
• remove(?) chapter 3
• add docstring exercise to 05-code-style.md
• add glossary at the end of each chapter #5
• add intro to collections
• download latest covid case data and change filename, update output in pandas chapter (non-essential)
• number all exercises
  • Lesson 1
  • Lesson 2
  • Lesson 3
  • Lesson 4
  • Lesson 5
  • Lesson 6
• ...

@ralves add to this list please