Updated configuration header.
HillEvent implements cancellable and now can retrieve all the hills.
Introduce new global variable in HillEvent, and remove implements
cancellable from HillChangeEvent because it is now an inherited method.
Add HillCreateEvent and HillRemoveEvent. The HillCreateEvent is
triggered when a player creates a hill using commands. The
HillRemoveEvent has not been given a trigger as of yet and is for the
moment, obsolete.