## Adds an event for when player presses a key.

### This mod is client- and server-side.

### Added functions are:
- `keyevent.register_on_keypress_bits([keys_to_be_pressed, ]func(keys, old_keys, dtime, player_name))`
  - `keys_to_be_pressed`: Optional. It can be a string, a table or a number.
  If any of these keys is changed, the event is triggered
  - `keys`: The pressed keys in bit format.
  - `old_keys`: The keys pressed before.
  - `dtime`: Time from last check.
  - `player_name`: Name of the player. Client-side this is `nil`.

- `keyevent.register_on_keypress([keys_to_be_pressed, ]func(keys, old_keys, dtime, player_name))`
  - Same as above but `keys` and `old_keys` is given in table format.