Added support for global hotkeys + example

[bibainet]

Added support for registering and handling global (system wide) hotkeys:

walk.RegisterGlobalHotKey(window, hotkeyID, walk.Shortcut {
    Modifiers: walk.ModControl | walk.ModAlt,
    Key: walk.KeyX,
})
window.Hotkey().Attach(func(hotkeyID int) {
    // Hotkey hotkeyID (Ctrl+Alt+X) pressed somewhere (may be in another application)
})

This functionality depended on changes from my recent pull request in lxn/win

Complete example included.

[lxn]

Hi Alexander,
I'm sorry for not responding to your PR for this long time. Are you still interested in getting this in?

[bibainet]

Hi Alexander,
I re-opened pull requests, but now there are merge conflicts that need to be resolved.

[lxn]

Thanks for reopening!

Do you think it would make sense to integrate this somehow with Action?

[bibainet]

May be. But I do not have much experience with WALK. I will not do this in the near future.

[lxn]

No problem. If you don't mind, I will have a look sometime soon.

[bibainet]

OK. Conflicts resolved.

[bibainet]

Hi, Alexander.
Should I do something else to complete the merge?

[lxn]

Hi Alexander,

Thank you for resolving the conflicts.

The question is if we should put this into Action, where I think it belongs, or leave it separate. I need to think some more about it, but right now there are more pressing issues on my mind, sorry. Hopefully next week.

[kgolding]

Hello - can I get an update of this as it's a feature I'm looking for please?

[shivas]

Would love this feature merged too