Added ability to render from Mustache String.

I wanted to have the ability to render Mustache Template coming from Pot Files. 
See this code extracted of an project we are doing with cake: 
```php
$v = new MustacheView();
$sessionLang = CakeSession::read('Config.language');
$this->setCurrentLanguage($person['Person']['locale']); // force language to Person locale
$v->view = __('user.people.new_password.message'); // instead of reading a .mustache file, render from translated string
$v->layout = false;
$v->renderFromString = true;  // tell Class MustacheView that rendering should be done from string
$v->set('user',$person['User']);
$v->set('url_login',FULL_BASE_URL . '/'. $person['Person']['locale'] .'/');
$v->set('url_create_newpassword',FULL_BASE_URL . '/'. $person['Person']['locale'] .'/password/createnew/');
$out = $v->render(); 
```   
You may integrate this modification into your branch...