Force-kill programs + bugfixes

Always repaint when toggling the altscreen

Restore Dragonfly support + BSD fix for Go 1.17

Fix BSD builds

StartReturningModel + ANSI compressor now opt-in

ANSI compressor and Program.Quit helper function

Windows: fix arrow keys + mouse support

Cancelable reads

Program.Send(msg) + better input handling

High performance rendering bugfix