ws/context: Increase write() visibility to public (#402)

This type is introduced to avoid confusion between the `.binary()` and `.write_raw()` methods on WebSocket contexts

src/ws/mod.rs

@@ -64,7 +64,7 @@ pub use self::client::{
     Client, ClientError, ClientHandshake, ClientReader, ClientWriter,
 };
 pub use self::context::WebsocketContext;
-pub use self::frame::Frame;
+pub use self::frame::{Frame, FramedMessage};
 pub use self::proto::{CloseCode, CloseReason, OpCode};
 
 /// Websocket protocol errors