Add Persistent::Vector[1,2,3] for creation

I would in general like to propose that custom data structure implementations add a Klass[] method for creation, this is in line with what Ruby itself does, and provides a uniform creation interface so implementations can be swapped more easily

```ruby
Array[1,2,3]
Hash[:foo => :bar]
Set[3,3,4]
Matrix[[1,2,3],[4,5,6]]
```