Provide Dockerfile

[gaul]

Fixes #120.

[gaul]

@bn0ir @dweinstein @joshdvir @ritazh @stevemayne I created a Dockerfile combining attributes from your implementations, including environment variable configuration and small size (50 MB). Please share your feedback!

One thing I would like to do is change the Dockerfile to use either master or the latest Sonatype snapshot. Any suggestions on how to do this without bringing a dev environment into the image?

[ritazh]

Do you mean something like this in the Dockerfile: RUN git clone -b master https://github.com/andrewgaul/s3proxy.git

[gaul]

@kahing suggests having Travis push the Docker image: https://sebest.github.io/post/using-travis-ci-to-build-docker-images/