Allow stack vertically the keys

[Phosphorus-M]

Hi, I usually when use plugins or tools like this I configure it to be vertically, for example in the plugin of OBS Input Overlay.

Is it feature possible to use with showmethekey?

Something like this:

[AlynxZhou]

Might be done when I have enough time.

[AlynxZhou]

I think I won't have enough time to do this at least in recent, but if anyone is willing to do this and send me a PR, I'll happy to review it.