[Feature Request] Enable vertical centering using keep_centered when scrolling

[fgimian]

Hey there, firstly thank you so much for your extension, it's absolutely awesome!!!

I was wondering if it would be possible to implement functionality similar to the Typewriter extension whereby enabling keep_centered will also keep the window centered while scrolling. Right now, MarkdownEditing only keeps the window centered while typing.

Thanks so much for your time 😄 Fotis