Support for object and callback defaults

[crazy4groovy]

Hi, I like this lib a lot; it reminds me of Groovy's support for default values:
https://blog.mrhaki.com/2012/10/groovy-goodness-create-list-with.html

There are a couple of interesting expansions you can consider with this lib:

1. Consider allowing objects to be defaults, not just literals. I assume this would mean the default cannot simply be passed back, but must first be assigned to target[property]. (However in order to avoid object reference hell, perhaps # 2 will help too.)

2. Accept a callback for the default option, that takes in the index and assigns the returned value (like a new object!) to that array item.