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.
First commit of list_lab. Done through 'Series 2'
list_lab.py should be done now.
Not sure if I've first-committed rot13.py yet. In any case, here it is...
Everything is getting a little intricate. Need to review code by printing/marking-up. Not at all done.
Added tests to rot13.py
rot13 and list_lab should be in final form
Merge branch 'master' of https://github.com/codefellows/sea-c15-python
Add dict_sets.py with initial dictionary
mailroom progress
Merge branch 'master' of https://github.com/codefellows/sea-c15-python

Pulling updates to local repo.
Add first few lines of dictionary edit and display calls
Will want to add some comments, but pretty much done...w
mailroom.py is done.
Minor PEP8 whitespace cleanup.
Merge remote-tracking branch 'upstream/master'
Remove dict_sets.py to repalce with dict_set.py
Add dict_set.py for 'Dict/Set Lab'
Add safe_input.py