tools/: moved get_key from atrf-path/gui.c to libatrf, for sharing

The old "raw" function becomes get_key_init. Calling get_key_init is
only necessary if one wants to control the moment standard input is
switched to raw mode. If get_key is invoked without a prior call to
get_key_init, it will initialize automatically.

- atrf-path/gui.c (raw, main): renamed "raw" to get_key_init
- atrf-path/gui.c (old_term, restore_term, get_key_init, get_key):
  moved to include/getkey.h and lib/getkey.c
- lib/getkey.c (get_key_init, get_key): made calling get_key_init
  optional
- lib/Makefile (OBJS): added getkey.o

tools/include/getkey.h

@@ -0,0 +1,19 @@
+/*
+ * include/getkey.h - Get single characters from standard input
+ *
+ * Written 2011 by Werner Almesberger
+ * Copyright 2011 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#ifndef GETKEY_H
+#define	GETKEY_H
+
+void get_key_init(void);
+char get_key(void);
+
+#endif /* !GETKEY_H */