Make vitamtp.h C++ friendly.

[codestation]

Please, add extern "C" in vitamtp.h so it can be imported in C++ projects easily. Without that, one has to add the extern keyword in every file that refers to the header.

#ifndef VitaMTP_h
#define VitaMTP_h

#ifdef __cplusplus
extern "C" {
#endif 
...
// vitamtp.h contents
...
#ifdef __cplusplus
}
#endif

#endif