Merge in "02-functions"

Merge branch "02-functions" into "develop"

Summary of the merged in commits:
 * 46439278: Adjust content overview in README.md
 * 0eb4b70a: Add review and exercises for notebook 02
 * 72db877c: Add initial version of notebook 02
 * ec3097e2: Add the sample_package folder to the project
 * c3fc760e: Add sample_module.py to the project
 * 22a85bc2: Streamline previous content
 * f6068383: Add numpy to the dependencies