Refactor screen_init(), use methods developed in pimd project

- Refactor screen_init()
  - use native impl. of TTY probing from pimd project
    - check if TIOCWINSZ works
    - check if we're running in watch(1), for initctl
  - check if ANSI goto(999,999) escape seq. works (invasive)
  - fallback to 80x24
- Drop screen_exit()
- Rename screen_init() to get_width(), for now, matching pimd
- Relocate call in main() to banner(), first fn to write to TTY

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/util.h

@@ -55,9 +55,7 @@ char *uptime       (long secs, char *buf, size_t len);
 
 char *sanitize     (char *arg, size_t len);
 
-void  screen_init  (void);
-void  screen_exit  (void);
-int   screen_width (void);
+int   screen_init  (void);
 
 static inline char *strterm(char *str, size_t len)
 {