fix compilation error in core_io.h

- error: 'vector' in namespace 'std' does not name a type
- add <vector> include in core_io.h
- remove <vector> includes from core_read.cpp and core_write.cpp

src/core_read.cpp

@@ -1,5 +1,4 @@
 
-#include <vector>
 #include "core_io.h"
 #include "core.h"
 #include "serialize.h"