Replace of Prosemirror with some smaller framework

[haiodo]

Prosemirror is a huge and pretty old, so let's check for something new.

• https://github.com/nenadpnc/cl-editor
  A demo at https://nenadpnc.github.io/cl-editor/ has a really nice in-place editing experience, and support Svelte.

• https://github.com/typewriter-editor/typewriter

[haiodo]

https://github.com/typewriter-editor/typewriter is svelte based.