Use int pin_mode instead of bool pullupActive in OneButton() constructor.

[IhorNehrutsa]

Use constructor:
OneButton(const int pin, const boolean activeLow = true, const int pin_mode = INPUT_PULLUP);
instead of:
OneButton(const int pin, const boolean activeLow = true, const bool pullupActive = true);

Use the given pin in input mode aka INPUT, INPUT_PULLUP, INPUT_PULLDOWN according to the Arduino board.
Like in the native Arduino function:

pinMode(pin, mode);

For example:

#if defined(BUTTONS_PULLUP)
userButton = new OneButton(aPIN);
//or it is equivalent to
userButton = new OneButton(aPIN, true, INPUT_PULLUP); 

#elif defined(BUTTONS_PULLDOWN)
userButton = new OneButton(aPIN, false, INPUT_PULLDOWN); 

#elif defined(BUTTONS_HIGH_IMPEDANCE)
userButton = new OneButton(aPIN, true, INPUT);
#endif

[IhorNehrutsa]

Hi @mathertel Matthias.
First, I am glad to see new commits in OneButton lib.

Last time I used OneButton lib with ESP32 microcontroller under Arduino framework in PlatformIO.
ESP32 has INPUT_PULLDOWN mode in
Arduino pinMode(pin, mode) function.

This PR allows to use all pin modes.
Could you please review the proposed changes and give your opinion on this PR.
I can also correct lib examples and documentation.

Best regards.
Ihor.