Switch to using pure ntdll calls for improved security

[dkrutsko]

As with #101, this issue relates to using system calls within ntdll.dll rather than kernel32.dll for slightly improved performance. While this is not always the most stable approach as these sometimes undocumented system calls may change, the calls used by robot have remained relatively stable throughout the last couple of years.

However, this might not be the most ideal change as some system calls, such as user32.dll cannot be translated to ntdll.dll calls, same with certain multimedia functions.