Methodnize response hash key value

Add Resonse#methodnize. 

To be checked:

* Hash key values are to be changed as method and return value
* Supports nested hash structure

To be discussed: 

* `resonse.a` will be `#<struct c=#<struct d=2>>` , when default hash is

```ruby
hash = { 
  a: {
     b: 1
  }
}
```
Is this desired return val?