Dobi should support the use of remote tar files, solo dockerfiles, and git URLs in the build context. This will allow projects to DRY their build process by building dockerfiles from dependencies without needing to manage the dependency itself.

Unfortunately there is no support in fsouza/go-dockerclient to do this for git repos (see fsouza/go-dockerclient#886). Without migrating to docker/docker/client (as per #89), the best way to handle this is (most likely) to use GetContextFromGitURL from docker/cli/cli/command/image/build to download the git repo into a temporary location on the local machine.

Handling dobi's enhanced caching for git repos and tar files is covered by #225