Add format:json operator

I've been finding this useful for debugging, and it kind of goes with the JSON operators

core/modules/filters/format/json.js

@@ -0,0 +1,28 @@
+/*\
+title: $:/core/modules/filters/format/json.js
+type: application/javascript
+module-type: formatfilteroperator
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Export our filter function
+*/
+exports.json = function(source,operand,options) {
+	var results = [],
+		spaces = null;
+	if(operand) {
+		spaces = /^\d+$/.test(operand) ? parseInt(operand,10) : operand;
+	}
+	source(function(tiddler,title) {
+		var data = $tw.utils.parseJSONSafe(title);
+		results.push(JSON.stringify(data,null,spaces));
+	});
+	return results;
+};
+
+})();