* implement plain syntax

* public api

* plain syntax

* public api

* plain syntax

* Update test/parser.ts

Co-authored-by: syuilo <Syuilotan@yahoo.co.jp>

* plain parser -> simple parser

* nomfm -> plain

Co-authored-by: syuilo <Syuilotan@yahoo.co.jp>

* fix link label matching

* 🚀
* add syntax rules of link label
* fix #104
* remove unnecessary applyParser() call