Handling non HTTP messages

[olanod]

Plugin writers should be able to add more than one handler that would process messages coming from an event bus or a different source of data. The one handler could also be just the custom message handler instead of an HTTP one.

// V1 HTTP request handler 
#[vlugin]
async fn http_handler(req: Request) -> Response {}

#[vlugin]
async fn my_data_handler(req: MyData) {}