This widget allows the user to set multiple variables in one go.

It thereby reduces code complexity that would arise when setting
many variables using "<$set>".

```
\define helloworld() Hello world!
<$vars greeting="Hi" me={{!!title}} sentence=<<helloworld>>>
  <<greeting>>! I am <<me>> and I say: <<sentence>>
</$vars>
```

How this Widget differs from the set widget:

 * Variables may be created by using the "key=value" notation
   that you already know from widgets like action-setfield.
 * You cannot specify a fallback ("emptyValue")
 * You cannot use a filter to produce a conditional variable assignement

Original discussion that led to the creation of this widget:
https://github.com/Jermolene/TiddlyWiki5/issues/1610

core/modules/widgets/vars.js

@@ -0,0 +1,75 @@
+/*\
+title: $:/core/modules/widgets/vars.js
+type: application/javascript
+module-type: widget
+
+This widget allows the user to set multiple variables in one go.
+
+```
+\define helloworld() Hello world!
+<$vars greeting="Hi" me={{!!title}} sentence=<<helloworld>>>
+  <<greeting>>! I am <<me>> and I say: <<sentence>>
+</$vars>
+```
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+var Widget = require("$:/core/modules/widgets/widget.js").widget;
+
+var VarsWidget = function(parseTreeNode,options) {
+	// Call the constructor
+	Widget.call(this);
+	// Initialise	
+	this.initialise(parseTreeNode,options);
+};
+
+/*
+Inherit from the base widget class
+*/
+VarsWidget.prototype = Object.create(Widget.prototype);
+
+/*
+Render this widget into the DOM
+*/
+VarsWidget.prototype.render = function(parent,nextSibling) {
+	this.parentDomNode = parent;
+	this.computeAttributes();
+	this.execute();
+	this.renderChildren(parent,nextSibling);
+};
+
+/*
+Compute the internal state of the widget
+*/
+VarsWidget.prototype.execute = function() {
+	// Parse variables
+	var self = this;
+	$tw.utils.each(this.attributes,function(val,key) {
+		if(key.charAt(0) !== "$") {
+			self.setVariable(key,val);
+		}
+	});
+	// Construct the child widgets
+	this.makeChildWidgets();
+};
+
+/*
+Refresh the widget by ensuring our attributes are up to date
+*/
+VarsWidget.prototype.refresh = function(changedTiddlers) {
+	var changedAttributes = this.computeAttributes();
+	if(Object.keys(changedAttributes).length) {
+		this.refreshSelf();
+		return true;
+	}
+	return this.refreshChildren(changedTiddlers);
+};
+
+exports["vars"] = VarsWidget;
+
+})();