clean up toString() and implement toJSON() consistently

core/src/processing/data/StringDict.java

@@ -475,17 +475,20 @@ public class StringDict {
   }
 
 
+  /**
+   * Return this dictionary as a String in JSON format.
+   */
+  public String toJSON() {
+    StringList items = new StringList();
+    for (int i = 0; i < count; i++) {
+      items.append(JSONObject.quote(keys[i])+ ": " + JSONObject.quote(values[i]));
+    }
+    return "{ " + items.join(", ") + " }";
+  }
+
+
   @Override
   public String toString() {
-    StringBuilder sb = new StringBuilder();
-    sb.append(getClass().getSimpleName() + " size=" + size() + " { ");
-    for (int i = 0; i < size(); i++) {
-      if (i != 0) {
-        sb.append(", ");
-      }
-      sb.append("\"" + keys[i] + "\": \"" + values[i] + "\"");
-    }
-    sb.append(" }");
-    return sb.toString();
+    return getClass().getSimpleName() + " size=" + size() + " " + toJSON();
   }
 }