Added update "column = !column"

Useful for changing booleans in DB.
Update like this:

...
$db->update("table", array("col_boolean" => $db->not()));

MysqliDb.php

@@ -477,6 +477,10 @@ class MysqliDb
                                 }
                             }
                             break;
+                        case '[N]':
+							if($val == null) $this->_query .= "!" . $column . ", ";
+							else $this->_query .= "!" . $val . ", ";
+							break;
                         default:
                             die ("Wrong operation");
                     }
@@ -754,6 +758,14 @@ class MysqliDb
         return Array ("[I]" => "-" . (int)$num);
     }
     
+    /**
+     * Method generates change boolean function call
+     * @param string column name. null by default
+     */
+    public function not ($col = null) {
+        return Array ("[N]" => (string)$col);
+    }
+
     /**
      * Method generates user defined function call
      * @param string user function body