* Replace build-essential in Docker builder image
build-essential is overkill, it pulls in all of the tools one needs to
make to build debian packages, which we are not doing. Even though this
is a builder image, it still takes time to download all the extra crud.
Replace build-essential with make gcc and g++, which are all that are
needed.
* Replace dev packages in final Docker image
The dev packages are only needed in the builder image. They add header
files and docs and things that are not needed in the final image.
Removing them and replacing them with just the runtime libraries reduces
the final image size by about 25% (160M->124M) in a local build.
Additionally, just for simplicity, zlib1g is already part of base
ubuntu minimal, so we don't even have to list it.
* Remove build-essential mention from the README
Just like the in Dockerfile, people don't need all of those packages
to build directly on their system.
Monty Taylor