message: Use altitude-hold PID controller
diff: #include <pidcontrollers/level.hpp>
  #include <pidcontrollers/yaw.hpp>
  #include <pidcontrollers/rate.hpp>
  +#include <pidcontrollers/althold.hpp>
  #include "SimReceiver.hpp"
  #include "SimBoard.hpp"
  @@ -27,10 +28,11 @@ class FHackflightFlightManager : public FFlightManager {
  private:
  - // PID tuning
  + // PID controllers
  hf::RatePid ratePid = hf::RatePid(0.225, 0.001875, 0.375);
  hf::YawPid yawPid = hf::YawPid(1.0625, 0.005625);
  hf::LevelPid levelPid = hf::LevelPid(0.20);
  + hf::AltitudeHoldPid altHoldPid = hf::AltitudeHoldPid();
  // "Board"
  SimBoard _board;
  @@ -72,6 +74,7 @@ class FHackflightFlightManager : public FFlightManager {
  _hackflight->addClosedLoopController(&ratePid);
  _hackflight->addClosedLoopController(&yawPid);
  _hackflight->addClosedLoopController(&levelPid);
  + _hackflight->addClosedLoopController(&altHoldPid);
  // Start Hackflight firmware, indicating already armed
  _hackflight->begin(true);
  