Add tap and hold actions for key remapping

[joseph-turk]

Description of the new feature / enhancement

Allow mapping keys to different actions when they are tapped vs when they are held, similar to QMK's Tap-Hold feature: https://github.com/qmk/qmk_firmware/blob/master/docs/tap_hold.md.

Scenario when this would be used?

The Capslock key is a convenient key for remapping, and currently I have it mapped to Ctrl. However, I also use vim keybindings in several places, and being able to use it as Esc when tapped would be nice.

[ZKBL]

This feature is also very helpful to me. Theoretically is it possible to add tap and long press options for all buttons. I am also looking for a solution for this.

This project jtroo/kanata implements similar functionality.

[JEFF-LIU-me]

Great feature. Similar to the (very popular) Mod Tap feature on Wooting keyboards.

• adds dedicated arrow keys and fn keys on 60% keyboards
• adds another layer to virtually the entire keyboard
• easier to remember than increasingly complicated shortcuts