chore(TypeScript): refactor objects into classes

fix: `Nil`(null, undefined) now renders as empty string
change: `parser.parseValue()` renamed to `parser.parseOutput`
change: registered tags/filters become static and shared across different liquid instances

test/unit/options/cache.ts

@@ -0,0 +1,44 @@
+import * as chai from 'chai'
+import * as mock from 'mock-fs'
+import Liquid from '../../../src/liquid'
+import * as chaiAsPromised from 'chai-as-promised'
+
+const expect = chai.expect
+chai.use(chaiAsPromised)
+
+describe('LiquidOptions#cache', function () {
+  let engine
+  beforeEach(function () {
+    engine = new Liquid({
+      root: '/root/',
+      extname: '.html'
+    })
+    mock({ '/root/files/foo.html': 'foo' })
+  })
+  afterEach(function () {
+    mock.restore()
+  })
+  it('should be disabled by default', function () {
+    return engine.renderFile('files/foo')
+      .then(x => expect(x).to.equal('foo'))
+      .then(() => mock({
+        '/root/files/foo.html': 'bar'
+      }))
+      .then(() => engine.renderFile('files/foo'))
+      .then(x => expect(x).to.equal('bar'))
+  })
+  it('should respect cache=true option', function () {
+    engine = new Liquid({
+      root: '/root/',
+      extname: '.html',
+      cache: true
+    })
+    return engine.renderFile('files/foo')
+      .then(x => expect(x).to.equal('foo'))
+      .then(() => mock({
+        '/root/files/foo.html': 'bar'
+      }))
+      .then(() => engine.renderFile('files/foo'))
+      .then(x => expect(x).to.equal('foo'))
+  })
+})