This adds a new optional parameter to screen.SetCursorStyle,
which is a color. The cursors demo is enhanced to show this.
This ability is supported on screen types, provided the underlying
terminal supports the capability.
This supports now curly, double, dashed, and dotted underline styles
where trhe terminal supports it. This works well on Windows Terminal,
reasonably on iTerm2, Alacritty, Kitty, and probably others.
The wasm mode terminal includes support for this, dependent on the browser
capabilities.
The macOS Terminal just changes the background color. Legacy Windows
console does nothing.
We will try to provide a regular underscore as a fallback. A new style.go
demo is included to see some style combinations.
Reverse video, not reverse text.
Provide an XTERM equivalent default palette.
Reset colors should go to silver on black.
Black color 0 should be rendered properly.