remark plugin to validate links to headings and files

Deprecated: this package is no longer maintained. Please use `remark-rehype` to move from remark (markdown) to rehype (HTML) and then replace `remark-slug` with [`rehype-slug`](https://github.com/rehypejs/rehype-slug).

remark plugin to configure it with YAML frontmatter

tap-producing test harness for node and browsers