Tag and CHANGELOG for 0.3.1 release

Make world blackboard static

This allows the blackboard to be used by systems that may not have access to the
ECS world, such as a scripting system that may not even be hooked into the game
update loop.

Update version for 0.3.0 release

update version for 0.2.6 release

update version for 0.2.5 release

bump gem version to 0.2.4

bump gem version to 0.2.3

bump version to 0.2.2

bump gem version

add changelog, bump version