Add SimpleGamepadFilter to the project.

SimpleGamepadFilter makes it easier to implement simple gamepad filters.
Add GamepadDeadzoneFilter to the project.

This filter applies a deadzone to gamepad joysticks.
Add GamepadConstantMultipleFilter to the project.

This filter multiplies the gamepad axes by a given value.
Add GamepadPowerFilter to the project.

This filter raises gamepad axes to a power while preserving their signs.