Use pygment's example_elixir.ex as a test case and for Color Settings Page demo text

Closes #11.

Use the pygment example_elixir.ex that @alco pointed me to on the elixir-lang mailing list so that I ensure I maintain feature parity with pygments, which is used in Github's code highlighting and this plugin because it's annoying if your source control highlighter and your dev tools disagree.