Test for repo.slug.

Slugs need tests as well.
Renaming test variables.

One letter variables are frowned on, in theory. Use a full word instead.
More test variables.

Renaming the `repo` variables.
String concatenation.

For string concatenation, use `+` instead of `.format()` for simple
cases, but use `.format()` for more complex string building.
Adding top level module docstring.

Adding in the top level overall module docstring.