PI controller with feedforward component

• init_controller(rate: float, min: float, max: float): PIControl
• set_gain(control: var PIControl, kp: float, ki: float, kf: float): void
• clear_gain(control: var PIControl): void
• pause_i(control: var PIControl): void
• resume_i(control: var PIControl): void
• update(control: var PIControl, sp: float, pv: float, f: float = 0.0): float