Add definitions from oleacc.h

[DataTriny]

Hello,

This PR adds all definitions from oleacc.h, as well as a new oleacc feature.

This is a requirement for UI Automation support, for which I already started the translation.

Things I am not really confident with are the function pointers on top of the file.

[mwcampbell]

The function pointer type declarations at the top of oleacc.rs (using the FN! macro) look OK to me, but then I'm new to Rust.

I notice a couple of problems with the pub fn declarations below:

1. They should be enclosed in extern "system", not extern "C", since they use the stdcall calling convention, not cdecl.
2. The functions that are declared using STDAPI in the C header file return an HRESULT; oleacc.rs currently declares no return types for those.

That's what I've found so far.