Improve rpc api return objects encoding

Signed-off-by: Lee Smet <lee.smet@hotmail.com>

src/models.rs

@@ -10,6 +10,6 @@ pub use actor::Actor;
 pub use context::Context;
 pub use flow::Flow;
 pub use job::Job;
-pub use message::Message;
+pub use message::{Message, MessageFormatType, MessageStatus, MessageType};
 pub use runner::Runner;
 pub use script_type::ScriptType;