[Meta] Add "Next", "Previous" and "Index" links in lessons? (Version 2)

[rgaiacs]

When designing the tools to handle the lessons after breaking up bc repo, #759, support "Next", "Previous" and "Index" links.

Suggestion

Pandoc support pass some variables when calling it (see -V) and we can use it to inform "Next" and "Previous" topic. Doing this with Make or bash looks a little difficult for me so, maybe, we need to use Python.

[rgaiacs]

I'm closing this since it is out of date (see swcarpentry/DEPRECATED-lesson-template#38).