Add windows-registry crate

[kennykerr]

This update adds the new windows-registry crate in the spirit of windows-result (#2847) and windows-version (#2702) to provide simple, safe, and efficient access to the Windows registry. The windows-registry crate takes advantage of the windows-result crate for error handling and works naturally with other windows-rs crates but does not depend on the larger windows or windows-sys crates.

Here's a simple example of reading registry key values:

use windows_registry::*;

fn main() -> Result<()> {
    let key = LOCAL_MACHINE.open(r#"SOFTWARE\Microsoft\Windows NT\CurrentVersion"#)?;
    println!("{}", key.get_string("ProductName")?);
    Ok(())
}

Here's an example of writing and reading values:

use windows_registry::*;

fn main() -> Result<()> {
    let key = CURRENT_USER.create(r#"software\\windows-rs"#)?;

    key.set_u32("number", 123)?;
    key.set_string("name", "Rust")?;

    println!("{}", key.get_u32("number")?);
    println!("{}", key.get_string("name")?);

    Ok(())
}

Here's an example of how you might recursively print keys and values:

use windows_registry::*;

fn main() -> Result<()> {
    let key = LOCAL_MACHINE.open(r#"SOFTWARE\Microsoft\Windows NT\CurrentVersion"#)?;
    print_tree(&key)?;
    Ok(())
}

fn print_tree(key: &Key) -> Result<()> {
    for subkey in key.keys()? {
        print_tree(&key.open(subkey)?)?;
    }

    for (name, value) in key.values()? {
        println!("{name}: {value:?}");
    }

    Ok(())
}

[ChrisDenton]

Nice! I think a brief top level example would be nice to have just to give people an idea of how to get started exploring the API.

[kennykerr]

I also added a readme example - thanks for the feedback Chris!