### New Features
- Added support for event batching via the event processor.
- Events generated by methods like `activate`, `track`, and `isFeatureEnabled` will be held in a queue until the configured batch size is reached, or the configured flush interval has elapsed. Then, they will be combined into a request and sent to the event dispatcher.
- To configure event batching, include the `eventBatchSize` and `eventFlushInterval` number properties in the object you pass to `createInstance`.
- Event batching is enabled by default. `eventBatchSize` defaults to `10`. `eventFlushInterval` defaults to `30000` in Node and `1000` in browsers.
- Added `localStorage` mitigation against lost events in the browser
- When event requests are dispatched, they are written to `localStorage`, and when a response is received, they are removed from `localStorage`.
- When the SDK is initialized for the first time in the browser, if any requests remain in `localStorage`, they will be sent, and removed from `localStorage` when a response is received.
- Updated the `close` method to return a `Promise` representing the process of closing the instance. When `close` is called, any events waiting to be sent as part of a batched event request will be immediately batched and sent to the event dispatcher.
- If any such requests were sent to the event dispatcher, `close` returns a `Promise` that fulfills after the event dispatcher calls the response callback for each request. Otherwise, `close` returns an immediately-fulfilled `Promise`.
- The `Promise` returned from `close` is fulfilled with a result object containing `success` (boolean) and `reason` (string, only when success is `false`) properties. In the result object, `success` is `true` if all events in the queue at the time close was called were combined into requests, sent to the event dispatcher, and the event dispatcher called the callbacks for each request. `success` is false if an unexpected error was encountered during the close process.
- Typed `getFeatureVariable` methods will still be available for use.