Event hooks ignore cancelled events by default
Add CONTRIBUTING.md, Update README.md
Merge pull request #73 from jacklin213/documentation

Add CONTRIBUTING.md, Update README.md
Merge pull request #67 from Marenwynn/master

Event hooks ignore cancelled events by default
Add VoxelVolume super-implementation for World and Chunk; moved methods from World and Chunk. Add EntityUniverse super-implementation with methods to get Entities