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

@@ -1,12 +1,12 @@
 import * as chai from 'chai'
 import * as mock from 'mock-fs'
-import Liquid from '../../../src'
+import Liquid from '../../../src/liquid'
 import * as chaiAsPromised from 'chai-as-promised'
 
 const expect = chai.expect
 chai.use(chaiAsPromised)
 
-describe('cache options', function () {
+describe('LiquidOptions#cache', function () {
   let engine
   beforeEach(function () {
     engine = new Liquid({

test/unit/options/strict.ts

@@ -1,10 +1,10 @@
-import Liquid from '../../../src'
+import Liquid from '../../../src/liquid'
 import * as chai from 'chai'
 
 const expect = chai.expect
 chai.use(require('chai-as-promised'))
 
-describe('strict options', function () {
+describe('LiquidOptions#strict_*', function () {
   let engine
   const ctx = {}
   beforeEach(function () {

test/unit/options/trimming.ts

@@ -1,11 +1,11 @@
 import * as chai from 'chai'
-import Liquid from '../../../src'
+import Liquid from '../../../src/liquid'
 import * as chaiAsPromised from 'chai-as-promised'
 
 const expect = chai.expect
 chai.use(chaiAsPromised)
 
-describe('trimming', function () {
+describe('LiquidOptions#trimming', function () {
   const ctx = { name: 'harttle' }
 
   describe('tag trimming', function () {