def key(key_name, *args, &block)
      member = Member.new(key_name, @_scope, *args, &block)
      @_members << member
      member
    end
def key(key_name, *args, &block)
      member = Member.new(key_name, @_scope, *args, &block)
      @_members << member
      member
    end
Public: Generates the start of the JSON member. Useful if the key you are
 generating is dynamic.

 key   - Used to generate the JSON member's key. Can be a String or Symbol.
 args  - An array of values passed to JSONBuilder::Value.
 block - Yielding any block passed to the element.

 Examples

   key :hello, 'Hi'
   # => "hello": "Hi"

   key "item-#{rand(0, 500)}", "I'm random!"
   # => "item-250": "I'm random!"

 Returns instance of JSONBuilder::Member.