Add "hidden" columns/fields into dbObject

dbObject.md

@@ -295,6 +295,42 @@ $products = product::arraybuilder()->paginate($page);
 echo "showing $page out of " . product::$totalPages;
 
 ```
+
+###Hidden Fields
+Sometimes it's important to block some fields that can be accessed from outside the model class (for example, the user password).
+
+To block the access to certain fields using the `->` operator, you can declare the  `$hidden` array into the model class. This array holds column names that can't be accessed with the `->` operator.
+
+For example:
+
+```php
+class User extends dbObject {
+    protected $dbFields = array(
+        'username' => array('text', 'required'),
+        'password' => array('text', 'required'),
+        'is_admin' => array('bool'),
+        'token' => array('text')
+    );
+
+    protected $hidden = array(
+        'password', 'token'
+    );
+}
+```
+
+If you try to:
+```php
+echo $user->password;
+echo $user->token;
+```
+
+Will return `null`, and also:
+```php
+$user->password = "my-new-password";
+```
+
+Won't change the current `password` value.
+
 ###Examples
 
 Please look for a use examples in <a href='tests/dbObjectTests.php'>tests file</a> and test models inside the <a href='tests/models/'>test models</a> directory

dbObject.php

@@ -124,6 +124,9 @@ public function __construct ($data = null) {
      * @return mixed
      */
     public function __set ($name, $value) {
+        if (property_exists ($this, 'hidden') && array_search ($name, $this->hidden) !== false)
+            return;
+
         $this->data[$name] = $value;
     }
 
@@ -135,7 +138,10 @@ public function __set ($name, $value) {
      * @return mixed
      */
     public function __get ($name) {
-        if (isset ($this->data[$name]) && $this->data[$name] instanceof dbObject)
+        if (property_exists ($this, 'hidden') && array_search ($name, $this->hidden) !== false)
+	    return null;
+
+	if (isset ($this->data[$name]) && $this->data[$name] instanceof dbObject)
             return $this->data[$name];
 
         if (property_exists ($this, 'relations') && isset ($this->relations[$name])) {
@@ -159,9 +165,8 @@ public function __get ($name) {
             }
         }
 
-        if (isset ($this->data[$name])) {
+        if (isset ($this->data[$name]))
             return $this->data[$name];
-        }
 
         if (property_exists ($this->db, $name))
             return $this->db->$name;