add option for working from buffers

[sdondley]

This is an attempt to address #24. I don't know lua well or how to create a test for this feature but if someone can offer some guidance, I will give it a shot.

How this patch works:

Somewhere in the nvim config, add let g:instant_work_from_buffer=1. Once enabled, files opened in the client will have the neovim buftype set to nofile and it will not be possibe to save the buffer open in the client. It is presumed the first client sharing the file(s) will have some kind of autosave feature to periodically save the file to the storage device when changes are made. I've been using the Pocco81/auto-save.nvim plugin at https://github.com/Pocco81/auto-save.nvim which seems to work well.

Now the client user can just quit the open buffer without worrying about ugly error messages.