Updated CacheManager to refuse class instantiation + Doc update

Author: Geolim4

docs/migration/MigratingFromV7ToV8.md

@@ -64,6 +64,22 @@ Calling `CacheManager::getStaticSystemDrivers()`
 #### :alarm_clock: Now:
 Replaced by `CacheManager::getDriverList()`
 
+### Removal of `ActOnAll` helper
+
+#### :clock1: Then:
+The helper `ActOnAll` used to be useful to act on all instance 
+
+#### :alarm_clock: Now:
+The "ActOnAll Helper" have been removed in profit of aggregated cluster support
+
+### Removal of `fallback` feature
+
+#### :clock1: Then:
+The `fallback` features used to be useful when a backend failed to initialize
+
+#### :alarm_clock: Now:
+Use aggregated cluster Master/Slave instead
+
 ------
 More infos in our comprehensive [changelog](./../../CHANGELOG.md).
 

lib/Phpfastcache/Api.php

@@ -24,13 +24,14 @@
  */
 class Api
 {
-    protected static $version = '3.0.0-rc2';
+    protected static $version = '3.0.0-rc3';
 
     /**
      * Api constructor.
      */
-    final private function __construct()
+    final protected function __construct()
     {
+        // The Api is not meant to be instantiated
     }
 
     /**
@@ -162,4 +163,4 @@ public static function getChangelog(): string
         }
         throw new PhpfastcacheIOException('The CHANGELOG_API.md file is not readable or has been removed.');
     }
-}
+}

lib/Phpfastcache/CacheManager.php

@@ -92,6 +92,14 @@ class CacheManager
      */
     protected static $badPracticeOmeter = [];
 
+    /**
+     * CacheManager constructor.
+     */
+    final protected function __construct()
+    {
+        // The cache manager is not meant to be instantiated
+    }
+
     /**
      * @param string $instanceId
      * @return ExtendedCacheItemPoolInterface