Added support to handle persistent living entities.
Updated Entity setRotation and getRotation to use Vector2f as entities

only use yaw and pitch but not roll.
Move Contribution Guidelines to SpongeDocs
Update Checkstyle and enable settings
Fix some of the checkstyle warnings
Move plugin workspace setup to SpongeDocs
The concept of environments.
Merge pull request #311 from CraftStone/master

The concept of environments.
Merge branch 'master' into entityAI

Conflicts:
	src/main/java/org/spongepowered/api/GameRegistry.java