* Add Step, ELU, SELU, Swish activation functions This commit adds the Step, ELU, SELU and Swish activations functions * add to the docs * review
* added leaky_relu relu6 softplus elu celu logsigmoid * minor fixes for docstring and benchmark imports * fixed elu implementation and added tests * added tests for optional param, changed leaky_relu param to fit pytorch documentation