include/: refactor header files

src/common/buf.c

@@ -1,4 +1,4 @@
-#include "buf.h"
+#include "common/buf.h"
 
 void buf_init(struct buf *s)
 {

src/config/rcxml.c

@@ -12,6 +12,7 @@
 
 #include "rcxml.h"
 #include "config/config-dir.h"
+#include "common/bug-on.h"
 
 static bool in_keybind = false;
 static bool is_attribute = false;

src/theme/xbm/parse.c

@@ -11,7 +11,7 @@
 #include <stdint.h>
 #include <stdbool.h>
 
-#include "buf.h"
+#include "common/buf.h"
 #include "theme/xbm/parse.h"
 
 /* TODO: should be window.active.button.unpressed.image.color */