Encode `conf_dict` to string.

def _encode_config(conf_dict):
    """Encode `conf_dict` to string."""
    out = []

    # get variables in order defined in settings._ALLOWED_MERGES
    for var in settings._ALLOWED_MERGES:
        out.append(conf_dict[var])

    # convert bools to chars
    out = map(
        lambda x: "t" if x else "f",
        out
    )

    return "".join(out)