Fix return codes for main()

src/main.c

 
 #include <stdio.h>
 
-#define LIGHT_RETURNVAL_INITFAIL  -2
-#define LIGHT_RETURNVAL_EXECFAIL  -1
+#define LIGHT_RETURNVAL_INITFAIL  2
+#define LIGHT_RETURNVAL_EXECFAIL  1
 #define LIGHT_RETURNVAL_SUCCESS   0
 
 int main(int argc, char** argv)