fix: better index.d.ts and a demo

The demo is located at demo/typescript/index.ts , working on #98

demo/nodejs/index.js

@@ -1,4 +1,4 @@
-const Liquid = require('../..')
+const Liquid = require('liquidjs')
 
 const engine = new Liquid({
   root: __dirname,

demo/typescript/index.ts

@@ -0,0 +1,13 @@
+import Liquid, {isTruthy} from 'liquidjs'
+
+const engine = new Liquid({
+  root: __dirname,
+  extname: '.liquid'
+})
+const ctx = {
+  todos: ['fork and clone', 'make it better', 'make a pull request'],
+  title: 'Welcome to liquidjs!'
+}
+
+// console.log('isTruthy:', isTruthy('a string here'));
+engine.renderFile('todolist', ctx).then(console.log)

demo/typescript/todolist.liquid

@@ -0,0 +1,5 @@
+<ul>
+  {% for todo in todos %}
+  <li>{{forloop.index}} - {{todo}}</li>
+  {% endfor %}
+</ul>