Implement "Bounce keys" feature

[kakurasan]

This PR adds the "Bounce keys" feature that allows users to ignore rapid, repeated keypresses of the same key.

My keyboard chatters and I really need the feature that works on Wayland desktops. I already wrote a standalone, python-evdev based implementation but I'd like to use evdevremapkeys' remapping feature at the same time.

Configuration example:

devices:
- input_name: 'SEM USB Keyboard'
  output_name: remap-kbd
  bouncekeys: 0.05
  remappings:
    ...

[Lillecarl]

FYI, the common language used for this is called "debounce", so naming it accordingly would make sense 😄