Merge branch 'ackermann'

The series.py and ackermann.py work is done.
Merge remote-tracking branch 'upstream/master'

Incorporating any changes from upstream master to my local
repository.
Added List Lab assignment
Fixed TODO of deleting all occurrences
Fixed like_dislike function
Added ROT13assignment
rot13 assignment ready for review
Rot13 - minor edits, now ready for review
List Lab assignment ready for review
Added Mail Room Madness assignment
First commit of list_lab. Done through 'Series 2'
list_lab.py should be done now.
Added more structure
Added dictionary
Added more structure
Not sure if I've first-committed rot13.py yet. In any case, here it is...
Changed structure
Everything is getting a little intricate. Need to review code by printing/marking-up. Not at all done.
Structure now working
Completed report function