add App::WebSocketRule_t

[CarloDG80]

Add App::WebSocketRule_t to clarify and simplify WebSocket creations.
Add some comments on crow::WebSocketRule<> class.

crow::SimpleApp::WebSocketRule_t& ws = CROW_WEBSOCKET_ROUTE(app, "/ws");

ws.onaccept([](const crow::request& /*conn*/, void** userData) -> bool
{
    // ...
    return true;
});
ws.onopen([](crow::websocket::connection& conn) {
    // ...
});
ws.onclose([](crow::websocket::connection& conn, const std::string& /*reason*/, uint16_t){
    // ...
});
ws.onmessage([](crow::websocket::connection& conn, const std::string& msgData, bool is_binary) {
    // ...
});

[gittiver]

Sorry, I don't see which problem this change shall solve.

[CarloDG80]

Technically it doesn't solve anything, but it simplifies and clarifies the object we're going to use.
Furthermore, in simple editors (like mine) the function tooltip doesn't appear on CROW_WEBSOCKET_ROUTE() macro.
My opinion, it is more clear
crow::SimpleApp::WebSocketRule_t& ws = ...
instead
crow::WebSocketRulecrow::SimpleApp& ws = ...

[gittiver]

Well, it does not harm anything and if it helps you, lets go with it.