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/parser/delimited-token.ts

@@ -0,0 +1,12 @@
+import Token from './token'
+
+export default class DelimitedToken extends Token {
+  trim_left: boolean
+  trim_right: boolean
+  constructor(raw, pos, input, file, line) {
+    super(raw, pos, input, file, line)
+    this.trim_left = raw[2] === '-'
+    this.trim_right = raw[raw.length - 3] === '-'
+    this.value = raw.slice(this.trim_left ? 3 : 2, this.trim_right ? -3 : -2).trim()
+  }
+}