input: add custom field to json data (#280)

closes #277

Author: dhimmel

schemas/input/csl-data.json

@@ -441,6 +441,15 @@
       },
       "year-suffix": {
         "type": "string"
+      },
+      "custom": {
+        "title": "Custom key-value pairs.",
+        "type": "object",
+        "description": "Used to store additional information that does not have a designated CSL JSON field. The note field can also store additional information, but custom is preferred for storing key-value pairs.",
+        "examples" : [
+          {"short_id": "xyz", "other-ids": ["alternative-id"]},
+          {"metadata-double-checked": true}
+        ]
       }
     },
     "required": ["type", "id"],