function is the wide-character equivalent
It copies at most n wide characters from the wide-character
string pointed to by src,
including the terminating L'\0' character,
to the array pointed to by dest.
Exactly n wide characters are
written at dest.
If the length wcslen(src) is smaller than n,
the remaining wide characters in the array pointed to
by dest are filled with L'\0' characters.
If the length wcslen(src) is greater or equal
to n, the string pointed to by dest will
not be L'\0' terminated.
The strings may not overlap.
The programmer must ensure that there is room for at least n wide
characters at dest.
returns a pointer to the last wide character written, that is,
dest + n - 1.