add an invite generator (#993)

* add an invite generator

* `number |= null` is safe, so we can simplify this

* Update Client.js

* aaaaaa

src/client/ClientDataResolver.js

@@ -190,6 +190,19 @@ class ClientDataResolver {
     return permission;
   }
 
+  /**
+   * Turn an array of permissions into a valid discord permission bitfield
+   * @param {Array} permissions An array of permissions as strings or permissions numbers (see resolvePermission)
+   * @returns {number}
+   */
+  resolvePermissions(permissions) {
+    let bitfield = 0;
+    for (const permission of permissions) {
+      bitfield |= this.resolvePermission(permission);
+    }
+    return bitfield;
+  }
+
   /**
    * Data that can be resolved to give a string. This can be:
    * * A string