Mismatch between documentation and implementation

[mjlassila]

The current Simplestats documentation instructs users to provide the end date for TOP n download counting using the parameter top_end_date when using the REST API but the implementation actually accepts top_stop_date.

As a result when a user provides the end date using the documented top_end_date parameter it is ignored. Because of that the API returns incorrect download counts including all data from the provided start date up to the current date instead of stopping at the intended end date.