Fix deheader warnings

Prior to this commit the output of deheader was:
	remove <stdlib.h> from ./jsmn.c
	in ./example/jsondump.c, realloc() portability requires <unistd.h>.
	in ./example/simple.c, strtol() portability requires <stdlib.h>.
	saw 4 files, 16 includes, 1 removable

example/jsondump.c

@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
 #include <string.h>
 #include <errno.h>
 #include "../jsmn.h"

example/simple.c

@@ -1,4 +1,5 @@
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include "../jsmn.h"
 

jsmn.c

@@ -1,5 +1,3 @@
-#include <stdlib.h>
-
 #include "jsmn.h"
 
 /**