Files

1. Read file line-by-line with Scanner
2. Read file line by line with Reader
3. Read file as one string (slurp)
4. Write to file
5. Write number to file
6. Append to file
7. Reading CSV file
8. Exercise: Sum of numbers in a file
9. Exercise: Count number of digitis
10. Exercise: ROT13 on file
11. Exercise: Selector with list of items from a file
12. TODO: Solution: Sum of numbers in a file