Treats hash keys as methods (getter/setter) #delegate

I would like to propose to treat Hash keys as methods in the method delegation through `delegate` when the target object `:to` is a Hash.

Example:

```ruby
  class Order < ActiveRecord::Base
    serialize :response
   
    delegate :code, :message, to: :response
   
    def place
      # ...
      response = json_response
      save
    end
  end

  order = Order.new # ...
  order.place
  order.code
  # => 200
  order.message
  # => Order created
```

Currently without this PR, I have to write boilerplate code to expose these values as methods.

```ruby
  class Order < ActiveRecord::Base
    serialize :response

    delegate :code, :message, to: :response_data
   
    def place
      # ...
      response = json_response
      save
    end

   def code; response[:code]; end
   def message; response[:message]; end
  end
```