* Add cache and cache purging Needed for https://github.com/rrweb-io/rrweb-snapshot/pull/85 * Add cache and cache purging Needed for https://github.com/rrweb-io/rrweb-snapshot/pull/85 * Cache addHoverClass as it is quite expensive https://github.com/rrweb-io/rrweb-snapshot/pull/85 * Make cache non-optional * Make cache required on addHoverClass