Merge branch '2-loss-function-api' into 'master'

Resolve "Loss function API"

Closes #2

See merge request !2

include/bodydynamics/factor/factor_inertial_kinematics.h

@@ -21,8 +21,8 @@ class FactorInertialKinematics : public FactorAutodiff<FactorInertialKinematics,
     public:
         FactorInertialKinematics(const FeatureBasePtr&   _feat,
                                  const StateBlockPtr&    _sb_bias_imu,
-                                 const ProcessorBasePtr& _processor_ptr = nullptr,
-                                 bool                    _apply_loss_function = false,
+                                 const ProcessorBasePtr& _processor_ptr,
+                                 bool                    _apply_loss_function,
                                  FactorStatus            _status = FAC_ACTIVE);
 
         virtual ~FactorInertialKinematics() { /* nothing */ }