Constant-time string comparison in Phalcon\Security::checkHash()

Fix #1755
Updated CHANGELOG
Phalcon\Security::deriveKey()

Generate a PBKDF2 key derivation of a supplied password
Test case
Optimization
Code fixes for PHP 5.6-dev and 5.7-dev
Phalcon\Forms\Form::hasMessagesFor() should return boolean

Fix #1764
Optimize Phalcon\Forms\Form::getMessagesFor()
Helper for Phalcon\Validation\Message\Group::__construct()
Optimize Phalcon\Forms\Form::getMessages()
Validate parameters in Phalcon\Forms\Form::setEntity()
Optimize Phalcon\Forms\Form::add()
Optimize Phalcon\Forms\Form::render()
Optimize Phalcon\Forms\Form::get()
Optimize Phalcon\Forms\Form::label()
Optimize Phalcon\Forms\Form::getLabel()
Optimize Phalcon\Forms\Form::has()
Bug fix in Phalcon\Forms\Form::remove()
Parameter validation in Phalcon\Mvc\Model\Message\Group::__set_state()
Native iterators for Phalcon\Forms\Form