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

i3bar/src/parse_json_header.c

@@ -10,19 +10,20 @@
  */
 #include "common.h"
 
-#include <stdlib.h>
-#include <unistd.h>
-#include <sys/types.h>
-#include <sys/wait.h>
-#include <signal.h>
-#include <stdio.h>
-#include <fcntl.h>
-#include <string.h>
-#include <errno.h>
 #include <err.h>
+#include <errno.h>
 #include <ev.h>
+#include <fcntl.h>
+#include <signal.h>
 #include <stdbool.h>
 #include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
 #include <yajl/yajl_common.h>
 #include <yajl/yajl_parse.h>
 #include <yajl/yajl_version.h>