Add double tap

[qwelyt]

KeyType{
    DoubleTap(Key, u8, Key),
// ...
}

If pressed once it works as normal key. If pressed and held, it works as a normal key.
If you double tap the key (press**press) within the time limit (u8) then it acts as key2.

How tap-tap&hold should be handled I'm not fully sure.

Perhaps there are several types hidden here.

KeyType {
   TapHold, // Press-Release-Press&Hold
   DoubleTap, // Press-Release-Press-Release
   DoubleTapHold, // Press-Release-Press-Release-Press&Hold
}

There are a lot of possibilities. Might be feature creep.