The class represents a serializer for frames and is implemented as
Cro::Transform that consumes Cro::WebSocket::Frame and produces
Cro::TCP::Message. It can be configured with a boolean parameter
mask. If set, this will mask the payload.
Everything that is needed for a complete serialization and is not specified in Cro::WebSocket::Frame instance is calculated inside of serializer: correct length is set, mask(if needed) is generated and the payload is masked.