Improved tree support and fixed lack of tree generation (fixes #101).
Fixed outer skin layers not appearing (fixes #162).
Fixed swords stopping digging in Survival mode (fixes #349).
Consider world created before WorldLoadEvent is called.
Added Eclipse project name override to build script.

Intended to fix weirdness with importing the files generated by the
Eclipse gradle plugin.
Added snow block placement handling.
Added note about Trello to CONTRIBUTING.md.