Auto-close the info window, when closing the current buffer.

[silky]

This is an attempt to make vim close if you exit while the info window is open; feel free to suggest ideas/alternatives/etc, this is basically a draft, but it is working well for me.

Note that there is a bug, I suppose, that it actually closes all quickfix windows upon exiting a single buffer, which is not ideal, because maybe you have a different split with a buffer and an info window for that open; in which case exiting one buffer closes all info windows.

I suppose to fix that one would need to identify the present buffer and match them based on names.

Is that important enough to do? Does anyone else even want this functionality at all?

This was inspired by: https://github.com/nvim-tree/nvim-tree.lua/wiki/Auto-Close#ppwwyyxx but I didn't bother with the additional complication :)

Notes:

• The command has to be Sync type, otherwise the present (last) buffer closes too fast and vim gets upset with E444: Cannot close last window.
• I updated the readme to make this the default behaviour if people copy and paste the config; but maybe because of the above caveat we shouldn't have that; it should just be an option for people that are willing to live with the annoyance.

cc @googleson78 .

[isovector]

LGTM. Thanks!