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

src/template/html.ts

@@ -0,0 +1,15 @@
+import Template from 'src/template/template'
+import Scope from 'src/scope/scope'
+import ITemplate from 'src/template/itemplate'
+import Token from 'src/parser/token'
+
+export default class extends Template implements ITemplate {
+  str: string
+  constructor(token: Token) {
+    super(token)
+    this.str = token.value
+  }
+  async render(scope: Scope): Promise<string> {
+    return this.str
+  }
+}