Introduce the ability to lookup an event.

Currently this will raise a 404 error when the event is not found, not sure if this is the desired way to handle or not.
Introduce scoreboards endpoint for fetching scoreboards.
Introduce lookup_author_ratings for getting ratings.
Adding the not-so-happy path for scoreboards.
Update README with additional examples.
README - formatting and consistency
Introduce Unloq::APIError::NotFoundError.

This will ease the path for integrators in rescuing 404s while letting other exceptions bubble up in certain methods, e.g. lookup_event