Deferred cache fixes, key check improvements, added cache/integration…

…-test

gc() and cleanExpired() tests

Added garbage collector

Set isHit (not isHit()) to true when CacheItem data is set, unsilence…

… warning

Updated test

updated phpunit.xml and composer.lock

FIX: expiresAfter() doesn't work properly when null value is passed

CacheItem read changes, ensure file is readable, unserialize only aft…

…er a positive read

Updated composer provide section

Initial commit