Improve Elixir Code Examples

[houllette]

The initial wave of Elixir code examples were very rudimentary at best, they could use some love and care.

This issue may need to be broken up into more specific examples that should be improved, but this will serve as the initial issue.

Something to keep in mind is the constraints of the quiz questions / examples that interface with the autograder as we don't want to break those.