Use async to simplify Mapscii.init()

src/Mapscii.js

@@ -43,8 +43,7 @@ class Mapscii {
     config = Object.assign(config, options);
   }
 
-  init() {
-    return new Promise((resolve) => {
+  async init() {
     if (!config.headless) {
       this._initKeyboard();
       this._initMouse();
@@ -53,8 +52,6 @@ class Mapscii {
     this._initRenderer();
     this._draw();
     this.notify('Welcome to MapSCII! Use your cursors to navigate, a/z to zoom, q to quit.');
-      resolve();
-    });
   }