Move word boxing structs to "mruby/boxing_word.h".

include/mruby/boxing_word.h

@@ -11,6 +11,16 @@
 # error MRB_INT16 is too small for MRB_WORD_BOXING.
 #endif
 
+struct RFloat {
+  MRB_OBJECT_HEADER;
+  mrb_float f;
+};
+
+struct RCptr {
+  MRB_OBJECT_HEADER;
+  void *p;
+};
+
 #define MRB_FIXNUM_SHIFT 1
 #define MRB_TT_HAS_BASIC MRB_TT_FLOAT
 

include/mruby/object.h

@@ -55,14 +55,4 @@ struct RFiber {
   struct mrb_context *cxt;
 };
 
-struct RFloat {
-  MRB_OBJECT_HEADER;
-  mrb_float f;
-};
-
-struct RCptr {
-  MRB_OBJECT_HEADER;
-  void *p;
-};
-
 #endif  /* MRUBY_OBJECT_H */