Submitting Week 5 Homework

I had a little trouble figuring out where there were good places for list comprehensions in the mailroom.py app. I had the same problem with tests; I wasn't sure how to utilize them when I'm not specifically checking the return value of a function. 

Aside from that, everything should be just about done
looks like you didn't quite get this one -- I"d take anotehr look, it's a good way to make sure you "get" functions as first class objects, and where keyword arguments get evaluated.