Expires entries in the cache.
Expired entries remain in the cache, but will be revalidated
after rendering.
By default, Unpoly automatically expires the entire cache whenever it processes
a request with a non-GET HTTP method. To customize this rule, use up.network.config.expireCache.
The server may also expire cache entries by sending an X-Up-Expire-Cache header.
Example
Calling without argument will mark the entire cache as expired:
up.cache.expire()
To only expire some cache entries, pass a URL pattern:
up.cache.expire('/users/*')
