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/click.c

@@ -9,12 +9,11 @@
  */
 #include "all.h"
 
-#include <time.h>
 #include <math.h>
-
-#include <xcb/xcb_icccm.h>
+#include <time.h>
 
 #include <X11/XKBlib.h>
+#include <xcb/xcb_icccm.h>
 
 typedef enum { CLICK_BORDER = 0,
                CLICK_DECORATION = 1,