1) Renumber the tasks (there were 2 'Task 3's)
2) In Task 3, use 'pos' instead of re-using 'newpos', to be consistent with
   Task 2
3) In Task 3, print out the decoded letter at the end
4) Remove rogue commas in the code in Task 5
Merge pull request #7 from jrmhaig/master

A few corrections in worksheet 3