Extract auth/login check into separate method
Add RequestError Exception to be more descriptive
Fix Piazza method name 'get.content' to 'content.get'
Extract shared Piazza API request code into separate method
Fix param default value error
Add get_users method to get specific users
Add get_instructor_stats method
Clarify docstring for get_instructor_stats
Add return value to docstring for get_instructor_stats
Add get_statistics_csv method for instructors