Parallelize asset loading

src/assets.js

@@ -8,15 +8,17 @@ export default class Assets {
   }
 
   async load() {
-    const tilesheet = new Image()
-    this.assetMap.tilesheet = tilesheet
-    tilesheet.src = "./assets/RPGpack_sheet.png"
+    return Promise.all([
+      this.loadImage("tilesheet", "./assets/RPGpack_sheet.png")
+    ])
+  }
 
-    return new Promise((resolve, reject) => {
-      tilesheet.addEventListener("load", e => {
-	console.log(e)
-	resolve()
-      })
+  loadImage(name, path) {
+    return new Promise(resolve => {
+      const img = new Image()
+      this.assetMap[name] = img
+      img.src = path
+      img.addEventListener("load", () => resolve(img))
     })
   }
 }