Floating windows in Neovim can now have footer

Originally posted on Reddit

After merging this PR, nvim_open_win() now supports footer and footer_pos options. They are symmetrical to title and title_pos options, but affect the bottom part of floating window border.

Important: this is a part of Neovim 0.10, not current stable Neovim 0.9.1. Will also be available in next Nightly build.

I am excited to see how Neovm community can leverage this. It seems like an appropriate place to show some help data alongside usual title. I have a few ideas for ‘mini.nvim’ myself :)