Release 0.4.0

Hotfix: Ensure multiple Pods don't get created for a GameServer

Since the cache is eventually consistent, there was a race condition
in which a GameServer could create more than one Pod backing it,
as the first one isn't found in the cache yet.

This sync's the cache before checking this value, so the cache
is up to date.

Changes for release 0.3.0

Needed to set the changelog version.

Release 0.3.0.rc

Release 0.2.0

Updates to docs, Changelog, etc for 0.2.0
release.

Release v0.2.0.rc

Includes and updated Changelog, update the install.yaml
to rc version, and updates for the docs for release.

Merge pull request googleforgames#131 from markmandel/doc/godoc-badge

Godoc badge!