Add support for `inccommand=split`

[jedevc]

Heya! Huge thanks for this plugin ❤️

When setting inccommand=split (to visualize changes across an entire file), for some reason, it seems to remain empty, while other changes in the main screen continue to be visualized (with a custom G command that maps to g):

The split works at intended in builtin commands like :s:

I could be missing something super super basic, sorry! I did see back in #7 (comment), that only visible lines in the buffer were being visualized, which might explain this? But I'd expect that if inccommand=split was set, that I'm okay to accept to the performance penalty.

Again, thanks! 🎉

[smjonas]

Heya! Huge thanks for this plugin ❤️

Hey, first of all thanks <3

I would have to add support for inccommand=split as it does not work out of the box when using Neovim's previewable command feature. This shouldn't be too hard.