Sort includes in *.c files

Not enabling in .clang-format because it breaks headers files.

Used:
    IncludeCategories:
      - Regex:           '^<config'
        Priority:        0
      - Regex:           '^".*"'
        Priority:        1
      - Regex:           '^<(xcb|xkb|yajl|X11)'
        Priority:        3
      - Regex:           '.*'
        Priority:        2

src/log.c

@@ -9,27 +9,27 @@
  */
 #include <config.h>
 
-#include <stdarg.h>
-#include <stdio.h>
-#include <string.h>
-#include <stdbool.h>
-#include <stdlib.h>
-#include <sys/time.h>
-#include <unistd.h>
+#include "i3.h"
+#include "libi3.h"
+#include "log.h"
+#include "shmlog.h"
+#include "util.h"
+
+#include <errno.h>
 #include <fcntl.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
-#include <errno.h>
+#include <sys/time.h>
+#include <unistd.h>
 #if !defined(__OpenBSD__)
 #include <pthread.h>
 #endif
 
-#include "util.h"
-#include "log.h"
-#include "i3.h"
-#include "libi3.h"
-#include "shmlog.h"
-
 #if defined(__APPLE__)
 #include <sys/sysctl.h>
 #endif