Adds a bit more error handling to analytics_report, updates documentation

* At present, in the event of an API error (such as Rate Limit Exceeded), the API will return a list of error objects as results, which means [get_leagues()] or [some_leagues] will never hit the or case. This adds a try/except to use a backup list of permanent leagues only if the API fails.
* Updates the documentation for analytics to show the new statistics (woot!)
* Updates the documentation for the items parsing code and the Item() class