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/wikirendertree.js

@@ -0,0 +1,91 @@
+/*\
+title: $:/core/modules/rendertree/wikirendertree.js
+type: application/javascript
+module-type: global
+
+Wiki text render tree
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Create a render tree object for a parse tree
+*/
+var WikiRenderTree = function(parser,options) {
+	this.parser = parser;
+	this.wiki = options.wiki;
+};
+
+/*
+Generate the full render tree for this parse tree
+	renderContext: see below
+An renderContext consists of these fields:
+	tiddlerTitle: title of the tiddler providing the context
+	parentContext: reference back to previous context in the stack
+*/
+WikiRenderTree.prototype.execute = function(renderContext) {
+	this.rendererTree = this.createRenderers(renderContext,this.parser.tree);
+};
+
+/*
+Create an array of renderers for an array of parse tree nodes
+*/
+WikiRenderTree.prototype.createRenderers = function(renderContext,parseTreeNodes) {
+	var rendererNodes = [];
+	for(var t=0; t<parseTreeNodes.length; t++) {
+		rendererNodes.push(this.createRenderer(renderContext,parseTreeNodes[t]));
+	}
+	return rendererNodes;
+};	
+
+/*
+Create a renderer node for a parse tree node
+*/
+WikiRenderTree.prototype.createRenderer = function(renderContext,parseTreeNode) {
+	var RenderNodeClass = this.parser.vocabulary.rendererClasses[parseTreeNode.type];
+	return new RenderNodeClass(this,renderContext,parseTreeNode);
+};
+
+/*
+Render as a string
+*/
+WikiRenderTree.prototype.render = function(type) {
+	var output = [];
+	$tw.utils.each(this.rendererTree,function(node) {
+		if(node.render) {
+			output.push(node.render(type));
+		}
+	});
+	return output.join("");
+};
+
+/*
+Render to the DOM
+*/
+WikiRenderTree.prototype.renderInDom = function(container) {
+	this.container = container;
+	$tw.utils.each(this.rendererTree,function(node) {
+		if(node.renderInDom) {
+			container.appendChild(node.renderInDom());
+		}
+	});
+};
+
+/*
+Update the DOM rendering in the light of a set of changes
+*/
+WikiRenderTree.prototype.refreshInDom = function(changes) {
+	$tw.utils.each(this.rendererTree,function(node) {
+		if(node.refreshInDom) {
+			node.refreshInDom(changes);
+		}
+	});
+};
+
+exports.WikiRenderTree = WikiRenderTree;
+
+})();