Introduce refactored wiki parser and renderer

This is a half-way through a big refactoring of the parsing and
rendering infrastructure. The main change is to separate the parse and
render trees, which makes the code a lot cleaner. The new parser isn't
yet functional enough to replace the existing parser so for the moment
you have to manually invoke it with `$tw.testNewParser()` in your
browser console. I really ought to use branches for this kind of
thing...

core/modules/widgets/view/viewers/wikified.js

@@ -0,0 +1,41 @@
+/*\
+title: $:/core/modules/widgets/view/viewers/wikified.js
+type: application/javascript
+module-type: newfieldviewer
+
+A viewer for viewing tiddler fields as wikified text
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+var WikifiedViewer = function(viewWidget,tiddler,field,value) {
+	this.viewWidget = viewWidget;
+	this.tiddler = tiddler;
+	this.field = field;
+	this.value = value;
+};
+
+WikifiedViewer.prototype.render = function() {
+	var parseTree;
+	// If we're viewing the text field of a tiddler then we'll transclude it
+	if(this.tiddler && this.field === "text") {
+		parseTree = [{
+			type: "widget",
+			tag: "transclude",
+			attributes: {
+				target: {type: "string", value: this.tiddler.fields.title}
+			}
+		}];
+	} else {
+		parseTree = this.viewWidget.renderer.renderTree.wiki.new_parseText("text/vnd.tiddlywiki",this.value).tree;
+	}
+	return this.viewWidget.renderer.renderTree.createRenderers(this.viewWidget.renderer.renderContext,parseTree);
+};
+
+exports.wikified = WikifiedViewer;
+
+})();