Don't handle collisions of staged files
Release version 0.3.0
Set version to 0.3.1-SNAPSHOT
Add failing test for #9
Merge branch 'master' into immutable-dockerfile

Conflicts:
	src/main/scala/sbtdocker/Dockerfile.scala
	src/test/scala/sbtdocker/DockerBuilderSpec.scala
Add mutable Dockerfile
Add compatibility with version 0.3.0