Foreign API documentation and small cleanup (#31)

* verify slate messages documentation

* rustfmt

* foreign API documentation

* rustfmt

controller/tests/file.rs

@@ -144,7 +144,7 @@ fn file_exchange_test_impl(test_dir: &str) -> Result<(), libwallet::Error> {
 
 	// wallet 2 receives file, completes, sends file back
 	wallet::controller::foreign_single_use(wallet2.clone(), |api| {
-		api.receive_tx(&mut slate, None, Some(sender2_message.clone()))?;
+		slate = api.receive_tx(&slate, None, Some(sender2_message.clone()))?;
 		adapter.send_tx_async(&receive_file, &mut slate)?;
 		Ok(())
 	})?;

controller/tests/repost.rs

@@ -132,7 +132,7 @@ fn file_repost_test_impl(test_dir: &str) -> Result<(), libwallet::Error> {
 	wallet::controller::foreign_single_use(wallet1.clone(), |api| {
 		let adapter = FileWalletCommAdapter::new();
 		slate = adapter.receive_tx_async(&send_file)?;
-		api.receive_tx(&mut slate, None, None)?;
+		slate = api.receive_tx(&slate, None, None)?;
 		adapter.send_tx_async(&receive_file, &mut slate)?;
 		Ok(())
 	})?;

controller/tests/self_send.rs

@@ -99,7 +99,7 @@ fn self_send_test_impl(test_dir: &str) -> Result<(), libwallet::Error> {
 		api.tx_lock_outputs(&slate)?;
 		// Send directly to self
 		wallet::controller::foreign_single_use(wallet1.clone(), |api| {
-			api.receive_tx(&mut slate, Some("listener"), None)?;
+			slate = api.receive_tx(&slate, Some("listener"), None)?;
 			Ok(())
 		})?;
 		slate = api.finalize_tx(&slate)?;