Added a download macro

This enables us to save changes by cooking a new tiddlywiki and forcing
a download of it

core/modules/macros/download.js

@@ -0,0 +1,52 @@
+/*\
+title: $:/core/modules/macros/download.js
+type: application/javascript
+module-type: macro
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+exports.info = {
+	name: "download",
+	params: {
+		title: {byName: "default", type: "text"},
+		type: {byName: true, type: "text"},
+		"filename": {byName: true, type: "text"},
+		"label": {byName: true, type: "text"}
+	},
+	events: ["click"]
+};
+
+exports.handleEvent = function(event) {
+	switch(event.type) {
+		case "click":
+			var text = this.wiki.renderTiddler(this.downloadType,this.downloadTitle),
+				link = document.createElement("a");
+			link.setAttribute("download",this.downloadFilename);
+			link.setAttribute("href","data:" + this.downloadType + "," + encodeURIComponent(text));
+			link.click();
+			event.preventDefault();
+			return false;
+	}
+	return true;
+};
+
+exports.executeMacro = function() {
+	this.downloadTitle = this.params.title || "$:/core/tiddlywiki5.template.html";
+	this.downloadType = this.params.type || "text/plain";
+	this.downloadFilename = this.params.filename || this.downloadTitle;
+	var attributes = {},
+		content = [];
+	if(this.hasParameter("label")) {
+		content.push($tw.Tree.Text(this.params.label));
+	} else {
+		content.push($tw.Tree.Text("Download \"" + this.downloadFilename + "\""));
+	}
+	return [$tw.Tree.Element("button",attributes,content)];
+};
+
+})();