Add dockerfiles to repo.
Update build_docker.sh and add instructions for building Docker images.
Add Docker usage example
Better emphasis on sections being files
Fix docker image tag
build_docker.sh: Exit on first failed command
Full heka+docker example
Dont name intermediary container for build
Grammar changes
Verify sha1sums in docker
Update Changelog with Docker changes
Use debian base image, to reduce size
Use COPY not ADD
Fix review items
Merge pull request #1067 from ecnahc515/dockerfile

Add Dockerfile(s) to Heka repo.