Refactors Liquid syntax highlighters to add line highlights.

Usage (ranges are space separated):

{% highlight js 1,4-6 %}
One range
Adds `highlight-line-active` to lines 1,4,5,6

{% highlight js 3-4 -1 %}
Two ranges (add/remove), remove is N/A
Adds `highlight-line-add` to lines 3,4

{% highlight js -1 3-4 %}
Two ranges (add/remove), add is N/A
Adds `highlight-line-remove` to lines 3,4

{% highlight js 3-4 5,8-10 %}
Two ranges, both are used
Adds `highlight-line-add` to lines 3-4
Adds `highlight-line-remove` to lines 5,8,9,10

_src/LiquidHighlight.js

@@ -0,0 +1,83 @@
+const HighlightLines = require('./HighlightLines');
+
+class LiquidHighlight {
+	constructor(liquidEngine) {
+		this.liquidEngine = liquidEngine;
+		this.hooks = [];
+		this.classHooks = [];
+	}
+
+	addHook(hookFunction) {
+		this.hooks.push(hookFunction);
+	}
+
+	addClassHook(hookFunction) {
+		this.classHooks.push(hookFunction);
+	}
+
+	getObject() {
+		let ret = function(highlighter) {
+			return {
+				parse: function(tagToken, remainTokens) {
+					let split = tagToken.args.split(" ");
+
+					this.language = split[0];
+					this.highlights = new HighlightLines(split.length === 2 ? split[1] : "");
+					this.highlightsAdd = new HighlightLines(split.length === 3 ? split[1] : "");
+					this.highlightsRemove = new HighlightLines(split.length === 3 ? split[2] : "");
+
+					this.tokens = [];
+
+					var stream = highlighter.liquidEngine.parser.parseStream(remainTokens);
+
+					stream
+						.on('token', token => {
+							if (token.name === 'endhighlight') {
+								stream.stop();
+							} else {
+								this.tokens.push(token); 
+							}
+						})
+						.on('end', x => {
+							throw new Error("tag highlight not closed");
+						});
+
+					stream.start();
+				},
+				render: function(scope, hash) {
+					let tokens = this.tokens.map(token => token.raw);
+					let tokenStr = tokens.join('').trim();
+
+					for( let hook of highlighter.hooks ) {
+						tokenStr = hook.call(this, this.language, tokenStr);
+					}
+
+					let lines = tokenStr.split("\n").map(function(line, j) {
+						let classHookClasses = [];
+						for( let classHook of highlighter.classHooks ) {
+							let ret = classHook(this.language, line, j);
+							if( ret ) {
+								classHookClasses.push(ret);
+							}
+						}
+
+						return '<div class="highlight-line' +
+							(this.highlights.isHighlighted(j) ? ' highlight-line-active' : '') +
+							(this.highlightsAdd.isHighlighted(j) ? ' highlight-line-add' : '') +
+							(this.highlightsRemove.isHighlighted(j) ? ' highlight-line-remove' : '') +
+							(classHookClasses.length ? " " + classHookClasses.join(" ") : "") +
+							'">' +
+							line +
+							'</div>';
+					}.bind(this));
+
+					return Promise.resolve(`<pre class="language-${this.language}"><code class="language-${this.language}">` + lines.join("") + "</code></pre>");
+				}
+			};
+		};
+
+		return ret(this);
+	}
+}
+
+module.exports = LiquidHighlight;