automatically enable "next" and "previous" buttons

[hannesdatta]

I need a way to show (automatically) "next page" and "previous page" buttons, e.g.

algorithm:
if _index.md or index.md file in a folder has the tag on-page-navigation: true

• show a "next page button" at the end of the page, pointing to the subsequent page (ordered by the page's weight attribute) in the current directory.
• show a "previous page button" at the end of the page, pointing to the previous page (ordered by page's weight attribute)

if any particular markdown file in the same folder has the attribute (overwrite) on-page-navigation: false, turn off next and previous buttons for that particular page only.