Text-only / seamless / single line / input mode

[Ghjuvan Lacambre]

Having a real Neovim GUI is nice for larger text areas, but it's not for smaller ones (e.g. Github's title input field). It'd be great if Neovim could be available in "text mode", meaning that that it would not spawn a frame but instead forward all inputs to the server and update the input field's content live as the underlying buffer is edited.

The implementation can probably copy whatever the neovim-in-{vscode,sublime,qtcreator,atom,...} extensions do.