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/rendertree/renderers/entity.js

@@ -0,0 +1,35 @@
+/*\
+title: $:/core/modules/rendertree/renderers/entity.js
+type: application/javascript
+module-type: wikirenderer
+
+Entity renderer
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Entity renderer
+*/
+var EntityRenderer = function(renderTree,renderContext,parseTreeNode) {
+	// Store state information
+	this.renderTree = renderTree;
+	this.renderContext = renderContext;
+	this.parseTreeNode = parseTreeNode;
+};
+
+EntityRenderer.prototype.render = function(type) {
+	return type === "text/html" ? this.parseTreeNode.entity : $tw.utils.entityDecode(this.parseTreeNode.entity);
+};
+
+EntityRenderer.prototype.renderInDom = function() {
+	return document.createTextNode($tw.utils.entityDecode(this.parseTreeNode.entity));
+};
+
+exports.entity = EntityRenderer
+
+})();