Add get api_key to __construct
Documentation updates
Add validate_theme_subtheme
Use new validate methods with get_by_subtheme. ref #16
Add new validate method and use it with get_by_year. ref #16
Use validation on search. ref #16
Get_wanted and get_owned updated
Get_by_number updated ref #16
Adapt for new request method
Fix remaining methods with validation. ref #16