[Feature Request] Add support for series

[rootkea]

Hello!

I'd like to be able to tag the front matter with a series attribute that will link related posts together and display that nicely in the post itself. An example of this is the Medium engineering growth series.

The elements of it are:

• a series URL
• a series metadata: title, URL, photo, and introduction and table of contents at the top of the post
• an epilogue with previews of the other articles in the series

Design inspiration for this (shows a sidebar, but I'd like it to be an epilogue instead; Medium actually does put this at the bottom when the screen is narrow).

[rootkea]

I came across the theme AllinOne which tries to implement series.

This is how series are displayed on the homepage:

This is a docker series page:

It's far from what I'd like to see but maybe this will help start discussion. :-)

PS - sorry, Go noob here. So can't help with the PR. :-(