Session04 Tasks

Task 1 - Dictionaries and Sets
Task 2 - Trigrams
Task 3 - Wrapper Function
Task 4 - Mailroom Madness
Per [PEP 8](https://www.python.org/dev/peps/pep-0008/#pet-peeves), there should not be whitespace, "immediately before the open parenthesis that starts the argument list of a function call."