Session 04 (complete)

It's common for python programs to allow you to stop them from running with `ctrl + c` and/or `ctrl + d`. Preventing this may frustrate users.

Additionally, returning `None` causes a `TypeError` on 91 after the following sequence occurs:

1. run mailroom.py
1. 1
1. ctrl + c
1. ctrl + c

This occurs because `request_user_input()` binds `None` to symbols (`thank_you_name` and `donation_amount`) that you're expecting to be specific types.