Add class 'GamepadDevice'. For normalized asignment of axis and button and Hot-Plug.

[HiroshiYAMA]

Each game controllers are assigned a different button number, so normalize it using the SDL2 library.

Requirement:

• 'sudo apt install libsdl2-dev'.
• -std=c++14

ex.)

auto gamepad = GamepadDevice::Create();
...
while (...)
{
  ...
  gamepad->Poll(1000);
  ...
  if (gamepad->IsAttached()) {
    if (gamepad->IsButtonDown()) {
      if (gamepad->GetButton_A == 1) {
        ... // Processing when button A is pressed.
      }
    }
  }
  ...
}