Deep extend

Hello!
This commit added new function, for extending big object as:

```js

var source = {
   auto: 1,
   moto: 1,
   boat: {
      fly: 0,
      cry: 1,
      subkey: {
      //... and so on
      }
   }
}

var object = {
   auto: 0,
   moto: 1,
   boat: {
      fly: 1,
      cry: 0,
      dry: {
          subkey: {
             //... and so on
          }
      },
      subkey: {
      //... and so on
      }
   }
}

```