Activation Functions

nn.X                                  # where X is ReLU, ReLU6, ELU, SELU, PReLU, LeakyReLU,
                                      # RReLu, CELU, GELU, Threshold, Hardshrink, HardTanh,
                                      # Sigmoid, LogSigmoid, Softplus, SoftShrink,
                                      # Softsign, Tanh, TanhShrink, Softmin, Softmax,
                                      # Softmax2d, LogSoftmax or AdaptiveSoftmaxWithLoss