Attributes for variables

[samharrison7]

Shouldn't be too difficult, just need to decide on syntax. Options include:

{
  "my_var": 42,
  "my_var@": {
    "attribute_name": "attribute_value",
    "another_attribute": "another_value"
  }
}

...or...

{
  "my_var": 42,
  "my_var@attribute_name": "attribute_value",
  "my_var@another_attribute": "another_value"
}

It might be worth thining about simplifying the specification of group attributes to match this:

{
  "my_group" : { ... }
  "my_group@attribute_name" : "attribute_value"
}