added explicitArrayProcessor

My specific case has to do with parsing iOS Xcode Storyboard XML, where tag names indicate whether the children will be single or multiple, e.g.
<scenes>
  <scene>
     <objects>
        <view>
          <subviews>
             <subview>
                ...

Using hard set explicitArray to 'true' requires accessing objects awkwardly:
storyboard.scenes[0].scene[0].objects[0].view[0]

Using hard set explicitArray to 'false' will make the code break in different scenarios, depending on whether the parent has a single child or multiple children:
storyboard.scenes[0].scene.objects // works when there's a single scene, breaks on multiple scenes
storyboard.scenes[0].scene[0].objects // ok when there are multiple scenes, breaks on single scenes

I added an option called explicitArrayProcessor that uses a function to determine whether a child element should be part in an array.
The function takes 2 parameters: the parent name and the child element

In my case I just check if the parent's name ends with an 's', and if so I assume child elements should be put in an array.

I think this can be useful in other scenarios as well.