Added ianblenke/docker-huginn as docker/ subdirectory

moved Dockerfile out of the root and renamed as Dockerfile.rbenv
Is it possible to automagically build this from the .env.example file at docker build time?

In the chef stuff we decided to go that way so that it would just magically pass through any new keys that were added/etc, without having to remember to always update docker when you update .env.example in master.