API: Events: Implement the 'redraw:update_line' event
API: Events: Implement the 'redraw:status_line' event
API: Events: Implement the 'redraw:ruler' event
API: Events: Implement the 'redraw:layout' event
API: Events: Implement the 'redraw:cursor' event
API: Implement vim_redraw_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.