Please add a way to pack string into msgpack bin type

[hanbing0715]

like said in title in msgpack-php we can unpack msgpack bin into php string but no way to pack string into msgpack bin how about add a option like msgpack-python's use_bin_type when it's true transfrom php string into msgpack bin

[maks-rafalko]

Quite surprised this is not implemented in the official PHP package.

For those who still need it: there is an implementation in pure PHP that has a feature to pack strings to bin type: https://github.com/rybakit/msgpack.php