Change EventObservers to use python lists/tuples instead of structs.
Change to use class rather than tuple for storing callback args.
Change callbacks list to use a linked list instead.
Add some docs.
Add args param to get_preoprty_observers.
Add new unbind_uid method to allow unbinding by matching a uid.
Add the unbind_uid code to EventDispatcher and Property.
Fix Observable to accept kwargs, and add unbind_uid support to make it compatible with current lang.
Add docs to unbind_uid.
Update lang to use unbind_uid instead of fast_unbind.
Fix unbind_uid callback.
Merge branch 'master' of https://github.com/kivy/kivy into bind-restore-list
Split appearent tuple assignment to two lines.
Merge pull request #2797 from matham/bind-restore-list

Restore internal EventObservers to use python objects instead of structs.