add instance support

[jackdotink]

Instances cannot be serialized into a buffer and as such must be treated with care. Instances should be sent in an array adjacent to the primary buffer payload. There are many cases where instances can turn into nil when sent over the network; zap should handle these cases with respect to if the instance is optional or not. Zap should provide users an API to put instances through many checks, from IsA to ChildName to Parent to IsDecendantOf.