Maps

1. Map (hash, dictionary)
2. Empty Map
3. Empty Map with make
4. Map type defintion without container
5. Create map with data in it already
6. Delete Map element
7. Size of map (len)
8. Access map element (that does not exist)
9. Map element exists
10. Increment map elements
11. Iterate over elements of map
12. Keys of a map
13. Sort map
14. Sort map by value
15. map of slices
16. Mixed map
17. Exercise: count characters
18. Exercise: count characters - sort by frequency
19. Exercise: count words
20. Exercise: count words from file
21. Solution: count characters
22. Solution: count characters - sort by frequency
23. Solution: count words
24. Solution: count words from file