Merge in "05-numbers"

Merge branch "05-numbers" into "develop"

Summary of the merged in commits:
 * 61f6981f: Add review and exercises for notebook 05
 * 76350cf8: Add section on the numeric tower
 * dbc3a67a: Streamline previous content
 * 6bebe70e: Adjust content overview in README.md
 * 4d6241cc: Add initial version of notebook 05
 * 3b28b8d5: Streamline previous content