Add extensions to send and receive serialized data on a websocket

[Kaliumhexacyanoferrat]

As a developer of an app using web sockets, I would like to easily send and received serialized objects via a web socket connection.

Example

Add extensions similar to the string extension we have.

connection.WriteAsync<T>(object, format = new JsonFormat()); // re-uses ISerializationFormat, defaults to JSON

.OnMessage((c, m) => m.DeserializeAsync<T>());

Acceptance criteria

• The functionality is directly implemented in the websocket module
• The ISerializationFormat is used
• If no format is specified, JSON is assumed
• Functionality is implemented as extensions (compare with ConnectionTextExtensions)
• The existing DataAsString extension is moved into an extension class (e.g. WebsocketFrameTextExtensions)
• The feature is documented on the GenHTTP website
• The feature is covered by acceptance tests