deprecate tuples as collection Recording pointers

[jacobagilbert]

This is done in favor of JSON objects, avoiding nested vectors (prohibited by flatbuffers) and also permitting expansion within this object.

[jacobagilbert]

@bhilburn collections support is ready for libsigmf, but it needs this specification change - can you take a look and provide thoughts?

[bhilburn]

Bumping, looks like no changes since last review

[jacobagilbert]

@bhilburn thanks for the ping. I think I have addressed most of the feedback. I also did a quick scan through this for object --> Object language and upgraded a number of uses to the proper Object form.