Increase lower bound of the vertical terminal size.
Fix the line-insert screen method.

It is now producing the correct DOM elements when inserting a string into
and existing segment with a different style.
Reset the alt screen when leaving alt mode.

Do this to avoid the flash-of-old-content when switching to alt mode again.
Do not set the LINES and COLUMNS env vars for the terminal child process.

This seems to confuse `htop` so that its resize does not work anymore.
Remove old render code.
Fix screen reset.

Adjust was not working for empty screens.
Fix resizing the terminal screen.

This time, compute cursor delta and origin offset correctly.