Some work on events and basic documentation

I added some basic documentation on every event for javadocs.

I also added an event, implemented an event, and changed three events.

PlayerPickupItemEvent: Event is called when a player pickups and item.
There is a problem with it as it will be called if your inventory is full and you stand on a item drop

PlayerDropItemEvent: I implemented this event into the InventoryHandler class

PlayerToggleSprintEvent, PlayerToggleSneakEvent: I made the sprint event cancelable and added the state of the toggle. (Whether or not they were sprinting/sneaking)

PlayerEatEvent: I added the item the player was trying to eat