Consider support for object / array unwrapping for extention

[codalogic]

One option to support object and array extension might be to adopt CDDL's Unwrapping mechanism (https://tools.ietf.org/html/draft-ietf-cbor-cddl-03#section-3.7).

Syntax can be decided on, but we could say that objects or arrays referred to with a rule name preceded by two dollar signs ($$) turns the object or array into a group (unwrapping it).

So:

$myseq = { "a" : integer, "b" : boolean }

$myextendedseq = { $$myseq, "c" : string }

Resulting in $myextendedseq being treated as:

{ ( "a" : integer, "b" : boolean ), "b" : string }

For objects, we could support auto-unwrapping (because it's not ambiguous). e.g.: just require (single $ char):

$myextendedseq = { $myseq, "c" : string }

The same can't be done for arrays.