@ updated version and description
@ implemented ability for sync message to be sent to multiple endpoints on the local net, but only one can actually receive the message
    @ changed Endpoint::Internal::recv
    + added protected public method Message::internal_clone
    + added protected public method SyncMessage::internal_clone
    @ changed Net::sendsync
    @ added field `valid` as Arc<Mutex<bool>> to SyncMessage
! fixed comment in SyncMessage for get_payload
! fixed bug where Message.clone did not properly clone canloop field