Add my three published plugins

[metalsmith-datamarkdown](https://github.com/majodev/metalsmith-datamarkdown) - Use markdown content within html tags via data-markdown attribute
[metalsmith-wordcount](https://github.com/majodev/metalsmith-wordcount) - Compute wordcount / average reading time
[metalsmith-headingsidentifier](https://github.com/majodev/metalsmith-headingsidentifier) - Add an id and anchor to all headings on a page. Ideal for permalinks.

BTW my first pull request ever! :)