Issue #22: Add a test for the can_cache option.
Merge pull request #23 from deviantintegral/can-cache-test

Issue #22: Add a test for the can_cache option.
Fix not adding timezone to dates.
Merge pull request #24 from deviantintegral/missing-date-gmt

Fix not adding timezone to dates.
Issue #22: Add $defaultTtl to CacheStorage constructor.
Merge pull request #25 from deviantintegral/cache-set-ttl

Issue #22: Add setDefaultTtl() to CacheStorage.
Fix stale-if-header not being added to max-age.