Adds Docker image building support.

[ackleymi]

Resolves #15

• To make these publicly available, run make build-docker to build the docker images then push them to a quickfixgo organization on hub.docker.com
• I'm open to potentially adding goreleaser for publishing docker images. It also automates other types of release publishing too (e.g- install examples via homebrew).

[cbusbey]

👍