Update README.md
updated World.deleteEntity to always try to remove the entity from the
"added" bag. This fixes a lot of NPEs when an entity is added and
deleted very quickly.
Merge branch 'master' of github.com:junkdog/artemis-odb
Updated changelog/contributors (#54).
Merge pull request #54 from Flet/npe-of-doom

updated World.deleteEntity to always try to remove the entity from the "added" bag.
Merge branch 'master' of github.com:junkdog/artemis-odb
Merge branch 'master' into cd-matrix