Add poisson likelihood

nifty4/library/__init__.py

@@ -5,5 +5,6 @@ from .nonlinear_wiener_filter_energy import NonlinearWienerFilterEnergy
 from .nonlinearities import Exponential, Linear, PositiveTanh, Tanh
 from .poisson_energy import PoissonEnergy
 from .unit_log_gauss import UnitLogGauss
+from .poisson_log_likelihood import PoissonLogLikelihood
 from .wiener_filter_curvature import WienerFilterCurvature
 from .wiener_filter_energy import WienerFilterEnergy