Bump windows to 0.51

[veeenu]

This PR bumps windows-rs to the latest 0.51 version.

There are some new patterns to deal with optional out params that windows isn't handling in a very elegant way, e.g. options of options of mutable pointers where the difference between None and Some(null_mut()) is not particularly evident, so some helper functions to deal with these cases should be added and applied:

• out_param for pre-allocated out parameters
• try_out_param for pre-allocated out parameters in a fallible function
• out_ptr for out pointers allocated by the function itself
• try_out_ptr for out pointers allocated by a fallible function

Example of usage:

let desc = try_out_param(|&mut out| device_and_swap_chain.GetDesc(out))?;

Blocked by #126

[veeenu]

While the new conventions in windows-rs are a bit verbose, they do feel more consistent, and having to repetitively instantiate None mutable options for storing pointers is easily (if not too elegantly) dealt with by using a couple simple helper functions.

Overall I'm very happy of this version bump because the code feels cleaner in the right spots and we can finally move on and stay aligned with new versions going forward.

As a mostly unrelated bonus, with this PR we officially compile on stable Rust and can finally drop the nightly requirement 🎉