Add new method to windows_registry::Key open_mut()

[ThalusA]

Suggestion

Hi,

It would be awesome if there was a way to open registry key with write access instead of only read access.
There is some case where I don't want to create it if it doesn't exist but I want to open my registry key with write access

[kennykerr]

Thanks for the suggestion - let me think about what that might look like.