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/value.ts

@@ -0,0 +1,30 @@
+import { evalExp } from 'src/render/syntax'
+import * as lexical from 'src/parser/lexical'
+import assert from 'src/util/assert'
+import Filter from './filter'
+import Scope from 'src/scope/scope'
+
+export default class {
+  initial: any
+  filters: Array<any>
+  constructor(str: string, strict_filters?: boolean) {
+    let match = lexical.matchValue(str)
+    assert(match, `illegal value string: ${str}`)
+
+    const initial = match[0]
+    str = str.substr(match.index + match[0].length)
+
+    const filters = []
+    while ((match = lexical.filter.exec(str))) {
+      filters.push([match[0].trim()])
+    }
+
+    this.initial = initial
+    this.filters = filters.map(str => new Filter(str, strict_filters))
+  }
+  value(scope: Scope) {
+    return this.filters.reduce(
+      (prev, filter) => filter.render(prev, scope),
+      evalExp(this.initial, scope))
+  }
+}