add support for 'Table of Contents'

[dlzht]

Thanks for this beautiful zola theme.

Zola support Table of Contents, is it possible for terminimal to have this feature too?

[pawroman]

Huh, I wasn't aware of this feature.

Where would the ToC go? In a post?

I would welcome a contribution that adds it as an optional feature. Wanna give that a go?

[DavidJS01]

Looking into contributing this next week

[AntoniosBarotsis]

I completely forgot this did not exist because I've implemented it in my blog.

Would adding it in the theme be as simple as my implementation? definition, usage.

Here's what it looks like rendered:

I have the page.extra.hide_toc check so I can disable the toc if I want to though I ended up not using that.

If it is roughly that simple I can just make a pr @pawroman