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/parser.ts

@@ -0,0 +1,43 @@
+import { ParseError } from '../util/error'
+import Liquid from 'src/liquid'
+import ParseStream from './parse-stream'
+import Token from './token'
+import Tag from 'src/template/tag/tag'
+import HTMLToken from './html-token'
+import TagToken from './tag-token'
+import OutputToken from './output-token'
+import Output from 'src/template/output'
+import HTML from 'src/template/html'
+import Value from 'src/template/value'
+
+export default class Parser {
+  liquid: Liquid
+
+  constructor(liquid: Liquid) {
+    this.liquid = liquid
+  }
+  parse (tokens: Array<Token>) {
+    let token
+    const templates = []
+    while ((token = tokens.shift())) {
+      templates.push(this.parseToken(token, tokens))
+    }
+    return templates
+  }
+  parseToken (token: Token, remainTokens: Array<Token>) {
+    try {
+      if (token.type === 'tag') {
+        return new Tag(token, remainTokens, this.liquid)
+      }
+      if (token.type === 'output') {
+        return new Output(token, this.liquid.options.strict_filters)
+      }
+      return new HTML(token)
+    } catch (e) {
+      throw new ParseError(e, token)
+    }
+  }
+  parseStream (tokens: Array<Token>) {
+    return new ParseStream(tokens, (token, tokens) => this.parseToken(token, tokens))
+  }
+}