Reorder and reorganize header files

Let the includes in the following order:

< system headers >
< libkmod >
< tool >
< local headers >
diff --git a/libkmod/libkmod-signature.c b/libkmod/libkmod-signature.c
index 96712e4..b7ef5f4 100644
--- a/libkmod/libkmod-signature.c
+++ b/libkmod/libkmod-signature.c
@@ -20,9 +20,9 @@
 
 #include <endian.h>
 #include <stdint.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <stdio.h>
 
 #include <shared/missing.h>
 #include <shared/util.h>