Add Guild#nameAcronym and make avatar/iconURLs into functions (#1144)

* Guild#iconURL(format, size);
* OAuth2Application#iconURL(format, size);
* User#iconURL(format, size);

src/structures/OAuth2Application.js

@@ -1,4 +1,5 @@
 const Snowflake = require('../util/Snowflake');
+const Constants = require('../util/Constants');
 
 /**
  * Represents an OAuth2 Application.
@@ -41,12 +42,6 @@ class OAuth2Application {
      */
     this.icon = data.icon;
 
-    /**
-     * The app's icon URL
-     * @type {string}
-     */
-    this.iconURL = `https://cdn.discordapp.com/app-icons/${this.id}/${this.icon}.jpg`;
-
     /**
      * The app's RPC origins
      * @type {?string[]}
@@ -122,6 +117,21 @@ class OAuth2Application {
     return new Date(this.createdTimestamp);
   }
 
+  /**
+   * A link to the application's icon
+   * @param {string} [format='webp'] One of `webp`, `png`, `jpg`, `gif`.
+   * @param {number} [size=128] One of `128`, '256', `512`, `1024`, `2048`
+   * @returns {?string} URL to the icon
+   */
+  iconURL(format, size) {
+    if (!this.icon) return null;
+    if (typeof format === 'number') {
+      size = format;
+      format = 'default';
+    }
+    return Constants.Endpoints.CDN(this.client.options.http.cdn).AppIcon(this.id, this.icon, format, size);
+  }
+
   /**
    * Reset the app's secret and bot token.
    * @returns {OAuth2Application}