Add preliminary Dat file saver

See https://datproject.org/ and https://beakerbrowser.com/

core/modules/savers/dat.js

@@ -0,0 +1,55 @@
+/*\
+title: $:/core/modules/savers/dat.js
+type: application/javascript
+module-type: saver
+
+Saves wiki using the Dat protocol (https://datproject.org/)
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Select the appropriate saver module and set it up
+*/
+var DatSaver = function(wiki) {
+	this.wiki = wiki;
+};
+
+DatSaver.prototype.save = function(text,method,callback) {
+console.log("Saving Dat")
+	dat.writeFile(document.location.protocol + "//" + document.location.hostname + ":" + document.location.port + document.location.pathname,text,"utf8").then(function(value) {
+		callback(null);
+	},function(reason) {
+		callback("Dat Saver Error: " + reason);
+	});
+	return true;
+};
+
+/*
+Information about this saver
+*/
+DatSaver.prototype.info = {
+	name: "dat",
+	priority: 3000,
+	capabilities: ["save", "autosave"]
+};
+
+/*
+Static method that returns true if this saver is capable of working
+*/
+exports.canSave = function(wiki) {
+	return !!window.dat;
+};
+
+/*
+Create an instance of this saver
+*/
+exports.create = function(wiki) {
+	return new DatSaver(wiki);
+};
+
+})();