fizzbuzz: Make fizzbuzz importable

Move the running stuff to an if, that only runs when we're running
standalone.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
Make hymns a proper module

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
gitignore .coverage

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
tests: Write & enable tests

Signed-off-by: Gergely Nagy <algernon@balabit.hu>