Macro multi_byte_range_tests

macro_rules! multi_byte_range_tests {
    (
        mod = $parentmod:ident,
        key = [$minkey:expr, $maxkey:expr], key < $keyubound:expr,
        value = [$minvalue:expr, $maxvalue:expr], value < $valueubound:expr
    ) => { ... };
}

Makes a common test suite for multi-byte range indices.