Investigate brotli compression

Apparently Brotli is a newish compression algorithm that is 25% smaller than gzip and has decent browser support. At a glance it’s not totally clear how easy it would be to actually enable—does not seem that CloudFlare has built-in support, so we would probably need to generate compressed assets on Travis and then figure out how to configure S3 to use the Brotli asset when the Accept header allows it. Also would need to make sure CloudFlare is varying the cache properly (and I think I might remember something about CF overwriting the Accept header to the origin?)

まず、issue で参照されているアセット生成およびデプロイのフローを追跡します。Travis、S3、CloudFlare、Accept ヘッダーの処理も含めます。Brotli を確実に有効化できるかどうかを確認し、キャッシュのバリエーションとブラウザーのサポートに関する考慮事項を含む、具体的な実装方針を文書化できれば完了です。