Return a list of the git configuration.

def git_list_config(repo_dir):
    """Return a list of the git configuration."""
    command = ['git', 'config', '--list']
    raw = execute_git_command(command, repo_dir=repo_dir).splitlines()
    output = {key: val for key, val in
              [cfg.split('=', 1) for cfg in raw]}
    # TODO(sam): maybe turn this into more easily navigable
    # nested dicts?
    # e.g. {'alias': {'branches': ..., 'remotes': ...}}
    return output