scroll_each API to work with batches like find_each

[willcosgrove]

The current Scroll API provides a method to iterate over each batch. But it does not provide a simple way of iterating over each element.

Much like ActiveRecord's find_in_batches has a corresponding find_each to hide away the batched nature of the iteration, I think scroll should have a corresponding scroll_each method. The name is debatable but it brought to mind the existing ActiveRecord API.

A simple implementation like this is what I'm imagining:

def scroll_each
  scroll do |batch|
    batch.each do |element|
      yield element
    end
  end
end

I'm happy to submit a PR if you're interested in something like this.