Add QueuedEventEmitter, use it for GuildSavedMessages events

src/QueuedEventEmitter.ts

@@ -0,0 +1,38 @@
+import { Queue } from "./Queue";
+
+type Listener = (...args: any[]) => void;
+
+export class QueuedEventEmitter {
+  protected listeners: Map<string, Listener[]>;
+  protected queue: Queue;
+
+  constructor() {
+    this.listeners = new Map();
+    this.queue = new Queue();
+  }
+
+  on(eventName: string, listener: Listener) {
+    if (!this.listeners.has(eventName)) {
+      this.listeners.set(eventName, []);
+    }
+
+    this.listeners.get(eventName).push(listener);
+  }
+
+  off(eventName: string, listener: Listener) {
+    if (!this.listeners.has(eventName)) {
+      return;
+    }
+
+    const listeners = this.listeners.get(eventName);
+    listeners.splice(listeners.indexOf(listener), 1);
+  }
+
+  emit(eventName: string, args: any[] = []) {
+    const listeners = [...(this.listeners.get(eventName) || []), ...(this.listeners.get("*") || [])];
+
+    listeners.forEach(listener => {
+      this.queue.add(listener.bind(null, args));
+    });
+  }
+}