API: Events: Implement the 'redraw_{fore,back}ground_color' events
API: Events: Implement the 'redraw:layout' event
API: Events: Implement the 'redraw:cursor' event
API: Events: Implement the 'redraw:win_end' event
API: Implement vim_request_screen to force redraw events
API: Implement vim_command_output function

This function can be used by API clients to execute a command and capture the
output.