Add storeEvents impl.

lib/store/memory.js

@@ -98,6 +98,17 @@ module.exports.MatrixInMemoryStore.prototype = {
      */
     scrollback: function(room, limit) {
         return [];
+    },
+
+    /**
+     * Store events for a room. The events have already been added to the timeline
+     * @param {Room} room The room to store events for.
+     * @param {Array<MatrixEvent>} events The events to store.
+     * @param {string} token The token associated with these events.
+     * @param {boolean} toStart True if these are paginated results.
+     */
+    storeEvents: function(room, events, token, toStart) {
+        // no-op because they've already been added to the room instance.
     }
 
     // TODO