msgpack-3.0.0RC1: prepare 3.0.0RC1
* Add support for PHP-8.1 Enums * merges #173 * fixes #171 * Add support for APCu * merges #162, #93 * Add OPT_ASSOC for roundtrip serialization of map. * merges #58
* Add support for PHP-8.1 Enums * merges #173 * fixes #171 * Add support for APCu * merges #162, #93 * Add OPT_ASSOC for roundtrip serialization of map. * merges #58