Simplify CString formatting

There is no static method such as CString::Format(). So instead of:

CString str;
str.Format(_T("%d"), i);

use:

CString StringFormat(LPCTSTR a_str, ...)
{
    va_list argptr;
    va_start(argptr, a_str);

    CString str;
    str.FormatV(a_str, argptr);

    return str;
}

Funny thing its stops working when you change LPCTSTR to CString.