support dictionary variables in match_dict

[sam-writer]

Honestly not sure if this is a great idea... We'd want to duplicate the match len(dict.items()) times, one for each entry. An example usage would be:

(resources/variables/lookups.json)

{
  "opposites": {
    "bad": "good",
    "small": {"IN": ["big", "long", "large"]}
  }
}

and in the match_dict:

resources/match_dicts/opposite_matches.json

...
  "not-opposite" : {
    "PATTERNS": [
      {
        "TEXT": "$LOOKUP:opposites.key"
      }
    ],
    "SUGGESTIONS": [
      [
        {
          "TEXT": "$LOOKUP:opposites.value"
        }
      ]
    ] 
  }

This would generate len(opposites.items()) entries in the match dict, copying the other properties like hooks and description.

Do we like this syntax? Other thoughts?