Builds the latest stable emacs in a docker image, packages it as
.tar.gz and then publishe a docker image to Docker Hub with emacs installed.
.deb package has no dependencies and there isn't an apt archive hosting it either.
Dockerfiles for other docker images:
git/Dockerfile: clone the emacs repo with git and build emacs.
amzn/Dockerfile: custom Amazon Linux 1 docker build
alpine/Dockerfile: alpine has up-to-date emacs versions.