Add a file system sync adaptor for the server

It's going to save tiddler changes to the file system

plugins/tiddlywiki/filesystem/filesystemadaptor.js

@@ -0,0 +1,54 @@
+/*\
+title: $:/plugins/tiddlywiki/filesystem/filesystemadaptor.js
+type: application/javascript
+module-type: syncadaptor
+
+A sync adaptor module for synchronising with the local filesystem via node.js APIs 
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+// Get a reference to the file system
+var fs = !$tw.browser ? require("fs") : null;
+
+function FileSystemAdaptor(syncer) {
+	this.syncer = syncer;
+}
+
+FileSystemAdaptor.prototype.getTiddlerInfo = function(tiddler) {
+	return {};
+};
+
+/*
+Save a tiddler and invoke the callback with (err,adaptorInfo,revision)
+*/
+FileSystemAdaptor.prototype.saveTiddler = function(tiddler,callback) {
+console.log("FileSystem: Saving",tiddler.fields);
+	callback(null,{},0);
+};
+
+/*
+Load a tiddler and invoke the callback with (err,tiddlerFields)
+*/
+FileSystemAdaptor.prototype.loadTiddler = function(title,callback) {
+console.log("FileSystem: Loading",title);
+	callback(null,{title: title, text: "Fake tiddler: " + title});
+};
+
+/*
+Delete a tiddler and invoke the callback with (err)
+*/
+FileSystemAdaptor.prototype.deleteTiddler = function(title,callback) {
+console.log("FileSystem: Deleting",title);
+	callback(null);
+};
+
+if(fs) {
+	exports.adaptorClass = FileSystemAdaptor;
+}
+
+})();