adds support for fn as a modifier key

[smithkyle]

The Fn key (at least on macOS) is actually a modifier key, so this commit adds support for it to be used as such...the only thing is...is that it doesn't actually seem to operate the same way as on the physical keyboard. For example, "Fn Backspace" should send "Delete", but it ends up just sending "Backspace" again. Based on my testing, "Fn" is being seen as a modifier, but it doesn't actually seem to be modifying. I'm not sure if this is the expected behavior since there are, indeed, separate keycodes for Backspace and Delete.

I initially came down this path hoping to get around the missing "Enter" keycode I implemented in #168. I was hoping I could just get around it by sending Fn + Return, but it didn't work. Based on how the other modifier keys are implemented, I believe I have implemented Function correctly, but have not seen the expected results.

Looking for some guidance... thanks!

[s1hofmann]

Hi @smithkyle 👋

I'm quite busy at the moment, will try to get back to you as soon as things calmed down.

Sorry for the delay

[smithkyle]

No problem at all! :)

[smithkyle]

It looks like some keys implicitly set the Fn modifier per this:

koekeishiya/skhd#1

But that doesn't explain why Fn+Backspace doesn't work...