Add QueuedEventEmitter, use it for GuildSavedMessages events

src/Queue.ts

@@ -0,0 +1,36 @@
+type QueueFn = (...args: any[]) => Promise<any>;
+
+export class Queue {
+  protected running: boolean = false;
+  protected queue: QueueFn[] = [];
+  protected timeout: number = 10 * 1000;
+
+  public add(fn) {
+    const promise = new Promise(resolve => {
+      this.queue.push(async () => {
+        await fn();
+        resolve();
+      });
+
+      if (!this.running) this.next();
+    });
+
+    return promise;
+  }
+
+  public next() {
+    this.running = true;
+
+    if (this.queue.length === 0) {
+      this.running = false;
+      return;
+    }
+
+    const fn = this.queue.shift();
+    new Promise(resolve => {
+      // Either fn() completes or the timeout is reached
+      fn().then(resolve);
+      setTimeout(resolve, this.timeout);
+    }).then(() => this.next());
+  }
+}