0.4.0 release

[maven-release-plugin] copy for tag v0.4.0-RC1

[maven-release-plugin] copy for tag v0.4.0-incubating-RC3

[maven-release-plugin] copy for tag v0.4.0-incubating-RC2

[maven-release-plugin] copy for tag v0.4.0-incubating-RC1

Tag for release 0.3.0-incubating

[maven-release-plugin] copy for tag v0.3.0-incubating-RC1

Release 0.2.0-incubating of Apache Beam.

This closes apache#776

[maven-release-plugin] copy for tag v0.2.0-incubating-RC2