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/strict.ts

@@ -0,0 +1,36 @@
+import Liquid from '../../../src/liquid'
+import * as chai from 'chai'
+
+const expect = chai.expect
+chai.use(require('chai-as-promised'))
+
+describe('LiquidOptions#strict_*', function () {
+  let engine
+  const ctx = {}
+  beforeEach(function () {
+    engine = new Liquid({
+      root: '/root/',
+      extname: '.html'
+    })
+  })
+  it('should not throw when strict_variables false (default)', function () {
+    return expect(engine.parseAndRender('before{{notdefined}}after', ctx)).to
+      .eventually.equal('beforeafter')
+  })
+  it('should throw when strict_variables true', function () {
+    const tpl = engine.parse('before{{notdefined}}after')
+    const opts = {
+      strict_variables: true
+    }
+    return expect(engine.render(tpl, ctx, opts)).to
+      .be.rejectedWith(/undefined variable: notdefined/)
+  })
+  it('should pass strict_variables to render by parseAndRender', function () {
+    const html = 'before{{notdefined}}after'
+    const opts = {
+      strict_variables: true
+    }
+    return expect(engine.parseAndRender(html, ctx, opts)).to
+      .be.rejectedWith(/undefined variable: notdefined/)
+  })
+})