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/child.c

@@ -10,25 +10,25 @@
 #include "common.h"
 #include "yajl_utils.h"
 
+#include <err.h>
+#include <errno.h>
+#include <ev.h>
+#include <fcntl.h>
+#include <paths.h>
+#include <signal.h>
+#include <stdarg.h>
+#include <stdio.h>
 #include <stdlib.h>
-#include <unistd.h>
+#include <string.h>
 #include <sys/types.h>
 #include <sys/wait.h>
-#include <signal.h>
-#include <stdio.h>
-#include <stdarg.h>
-#include <fcntl.h>
-#include <string.h>
-#include <errno.h>
-#include <err.h>
-#include <ev.h>
-#include <yajl/yajl_common.h>
-#include <yajl/yajl_parse.h>
-#include <yajl/yajl_version.h>
-#include <yajl/yajl_gen.h>
-#include <paths.h>
+#include <unistd.h>
 
 #include <xcb/xcb_keysyms.h>
+#include <yajl/yajl_common.h>
+#include <yajl/yajl_gen.h>
+#include <yajl/yajl_parse.h>
+#include <yajl/yajl_version.h>
 
 /* Global variables for child_*() */
 i3bar_child child;