Use Types::Serialiser::Boolean for true/false

[wisnij]

Could Types::Serialiser::Boolean be used rather than defining Data::MessagePack::Boolean internally? Using and checking for that during conversion would make interoperability with other serialization formats a lot easier. In particular, it would be a big win to be able to convert from JSON text to Perl data and then into MessagePack, and vice versa, without having to account for the boolean types manually.