[PATCH] include: Add xact3.h

[Vijay Kiran Kamuju]

Based on work by Ethan Lee and Alistair Leslie-Hughes
Use the header file directly instead of idl file just like other
directx headers like dsound.h
Implementing idl file involves a lot of hacks.

Signed-off-by: Vijay Kiran Kamuju <infyquest(a)gmail.com>