grading hw4

Grade: 4.3/5
Hi Paul,
Your code looks pretty solid.  I left a lot of inline comments for you.  The feedback I give you if suggestions that most people would generally agree are good design suggestions, and if you keep them in mind, people will find your code easier to work with.  That said, please keep in mind that the code is good.  
Anyways, awesome work. Once you've read the comments, make a comment to the pull request or send me an email. Afterwards, close the PR (and optionally delete the graded branch), and we'll give you another 0.5 points.