docs: add some TODOs for the next major release

Author: darrachequesne

lib/socket.ts

@@ -10,6 +10,7 @@ const debug = debugModule("engine:socket");
 
 export class Socket extends EventEmitter {
   public readonly protocol: number;
+  // TODO for the next major release: do not keep the reference to the first HTTP request, as it stays in memory
   public readonly request: IncomingMessage;
   public readonly remoteAddress: string;
 

lib/transports/polling.ts

@@ -75,6 +75,7 @@ export class Polling extends Transport {
       debug("request overlap");
       // assert: this.res, '.req and .res should be (un)set together'
       this.onError("overlap from client");
+      // TODO for the next major release: use an HTTP 400 status code (https://github.com/socketio/engine.io/issues/650)
       res.writeHead(500);
       res.end();
       return;
@@ -116,6 +117,7 @@ export class Polling extends Transport {
     if (this.dataReq) {
       // assert: this.dataRes, '.dataReq and .dataRes should be (un)set together'
       this.onError("data request overlap from client");
+      // TODO for the next major release: use an HTTP 400 status code (https://github.com/socketio/engine.io/issues/650)
       res.writeHead(500);
       res.end();
       return;