Parent method

So here is the parent method. It correctly returns the parent of the current slot. Unfortunately that makes its behavior a little different than the Shoes3 behavior.

### Same
*  They both return the parent object

### Different
* 
```ruby
Shoes.app do
  para parent
end
```
returns nothing in Shoes3, and returns the InternalApp in Shoes4

* `para parent` in Shoes3 `para Object`  returns a string with the object's class in it: `(Shoes::Flow)`. This isn't how para does objects in Shoes4. But I suspect this difference has little to do with para . . .