Updating Block event with reference to Voxel

Updated `BlockEvent` with `Voxel getVoxel()` for block/position. I'm debating
renaming the events to `VoxelEvent` but that may be too different from
what devs are accustomed to.

Add cancel based methods to event base interface

Add ItemsStack interface, without any Inventory

Fixed javadoc, added missing @Overrides
Merge branch 'master' of https://github.com/zeuslightning125/SpongeAPI

Conflicts:
	src/main/example/main/java/org/spongepowered/example/ExamplePlugin.java