Encode bson.code.Code.

def _encode_code(name, value, dummy, opts):
    """Encode bson.code.Code."""
    cstring = _make_c_string(value)
    cstrlen = len(cstring)
    if not value.scope:
        return b"\x0D" + name + _PACK_INT(cstrlen) + cstring
    scope = _dict_to_bson(value.scope, False, opts, False)
    full_length = _PACK_INT(8 + cstrlen + len(scope))
    return b"\x0F" + name + full_length + _PACK_INT(cstrlen) + cstring + scope