3.1.0

Symfony HttpCache

• Add events PRE_FORWARD and POST_FORWARD to allow event listeners to alter
  the request before and after it is sent to the backend.
• Changed CustomTtlListener to use the POST_FORWARD event instead of
  PRE_STORE. Using PRE_STORE, requests that are not considered cacheable by
  Symfony were never cached, even when they had a custom TTL header.
• Add flag fallbackToSmaxage to CustomTtlListener to allow controlling
  fallback to s-maxage if custom TTL header is not defined on the response.
• Fix: Do not call store if Response object is not longer cacheable after event
  listeners. If you use the custom TTL system, this is only a performance
  improvement, because the TTL of the response would still be 0. With a custom
  listener that changes the response explicitly to not be cached but does not
  change s-maxage, this bug might have led to caching responses that should not
  have been cached.