Rename WindowStage to RetransmitStage

The window is used for both broadcasting from leader to validator
and retransmitting between validators.

src/lib.rs

@@ -40,6 +40,7 @@ pub mod request;
 pub mod request_processor;
 pub mod request_stage;
 pub mod result;
+pub mod retransmit_stage;
 pub mod rpu;
 pub mod service;
 pub mod signature;
@@ -54,7 +55,6 @@ pub mod tvu;
 pub mod vote_stage;
 pub mod voting;
 pub mod wallet;
-pub mod window_stage;
 pub mod write_stage;
 extern crate bincode;
 extern crate bs58;