fix(header): read description delimiter exactly as ": "

PR: #1

fix: set header during descriptionToken instead of bodyToken

feat!: use lexical analyzer instead of regex

* remove IsHeaderErr, IsNoBlankLineErr
* add more test cases, update benchmark
* update README, LICENSE, comments

docs: update README

docs: update links in README

docs: update README

docs: update README

regex perf

feat: add IsHeaderErr

docs: update readme and license file