Suggestions for new docking features

Dear developers: I'm not very familiar with GitHub, so I don't know which section I should use to send you suggestions for new features. Maybe I can do this by creating an issue. I hope Nuklear can have a window docking feature like ImGui's docking branch, allowing one window to be docked into another. This would be a huge help for developers like us who are working on our own game engines.

The issue names no file, test, or entry point. Start by reviewing the Nuklear repository and ImGui's docking branch to clarify the desired docking behavior; done requires a defined scope and agreed implementation plan.

Written by the indexing model from the issue text.