Improve compiler compatibility (#743)

* fix returns

* use standard C headers

* struct/class mismatch

* explicit this in template

* switch variable scope

* C standard compliance

* & l-value

include/JSystem/JAudio/JAIAnimation.h

@@ -3,7 +3,7 @@
 
 #include "dolphin/types.h"
 
-class Vec;
+struct Vec;
 class JAISound;
 class JAIBasic;
 namespace JAInter {