- expand section on indexing and slicing in Chapter 1 on arrays
- add section on dimensionality and shapes of arrays
- streamline text in Chapter 1
- include thumbnails in links to scientific libraries
- add explanation on slicing to core Python introduction
  and adjust the list example
- streamline some text and titles in Chapter 0

- Classification is now Chapter 3
- New Chapter 2: Time Series Analysis

- make many small notebooks out of one big one
- introduce folder structure for all chapters
- add a bit more content to Chapter 0
- streamline text in Chapter 0
- adjust table of contents

- jupyterlab => ^3.1
- matplotlib => ^3.4
- numpy => ^1.21
- pandas => ^1.3
- scikit-learn => ^1.0
- various transient dependencies

- add 2020
- rename the LICENSE file into LICENSE.txt