Improve compatibility with PHP 7.4 (cakephp#161)

Improve compatibility with PHP 7.4

Merge pull request cakephp#158 from vmikhav/fix/fix-component-constru…

…ctor

Fix component's constructor error message

Merge pull request cakephp#156 from johanmeiring/fix-shell-assignment

Assign shell via new setter instead of directly

Merge pull request cakephp#154 from johanmeiring/patch-1

Add $Shell and $controller properties to AclExtras

Update README.md

Acl 0.3.3

* Use string class names to get methods. This fixes errors when
  controllers do work in their constructors.

Acl 0.3.2

* Remove use of non-existant DbConfig task

Acl 0.3.1

* Complete deprecation updates for 3.6.0

Acl 0.3.0

* Fix compatibility with CakePHP 3.6.0