Squashed commits:

Created DockerPea class that wraps docker-api. Using VCR to mock Docker

Docker API working against all docker interactions apart from buildstep

Docker Remote API fully implemented. Just needs tests for builder

Specs for using Buildstep via Docker Remote API

Bumped version to 0.0.3. Added CHANGELOG.md. Also note that this fixes #4
Make use of last_message clearer
Travis dance