Add $mref to inst variables

[dhower-qc]

Also enhances arch_gen to expand references.

Supports $ref (JSON Reference) and $mref (merged ref, doesn't ignore other keys in the object)

Difference:

(in something.yaml)
key:
  ref_extra: Hello!

obj:
  $ref: path/to/something.yaml#/key
  extra: Hi!

=> obj = { ref_extra: "Hello!" }

obj:
  $mref: path/to/something.yaml#/key
  extra: Hi!

=> obj = { extra: "Hi!", ref_extra: "Hello!" }

[drom]

$ref is immutable reference. $mref will create new object similar to the original.
We need to clearly delineate use cases for $ref and $mref

[dhower-qc]

Good point. The way I see it, $ref is a pointer, and $mref is inheritance. For example, @james-ball-qualcomm is using $mref to represent profiles that build on each other (RVA20 -> RVA22).

[james-ball-qualcomm]

That is the plan and I'll be doing this soon. So, I'll find out how $mref works for profiles.

[dhower-qc]

Moving to discussion #247