Can it add an invisible <a> tag into each heading tag (h2~h6), when converting md to html?

[Zhaopudark]

I usually use this module to make up a Pandoc filter and apply it when using hexo with hexo-renderer-pandoc.

I have found it will be very helpful if it can add an invisible header link (<a>) into each header (<h2>~<h6>) when rendering md to HTML.

For example, the original md is as:

## test

And the expected HTML after converting is as:

<h2 id="test"><a href="#test" class="headerlink" title="test"></a>test</h2>

Can this module support it?

[Zhaopudark]

The PR #4 has realized this feature.

Note, in PR #4, all headers (<h1>~<h6>) will be inserted with an invisible header link.

Sometimes, in some renderers/frameworks/tools, the <h1> will be considered specially to form a title. But we hold the view that, in most cases, this special behavior does not conflict with PR #4 in terms of the visible effects. So, we make PR #4 influence all headers (<h1>~<h6>) for simplification, instead of ignoring <h1>.