Switch to stdbool.h

- Add `#include <stdbool.h> to all files previously using the
   `TRUE`/`FALSE` macros
 - Replace all instances of `TRUE`/`FALSE` with `true`/`false`,
   respectively
 - Definitions of `TRUE`/`FALSE` macros retained in wiringPi.h for compatibility.

examples/Gertboard/vumeter.c

@@ -18,16 +18,12 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdbool.h>
 #include <sys/time.h>
 
 #include <wiringPi.h>
 #include <gertboard.h>
 
-#ifndef	TRUE
-#define	TRUE	(1==1)
-#define	FALSE	(!TRUE)
-#endif
-
 #define	B_SIZE	1000
 #define	S_SIZE	 128