Abstract activation and implement softmax

include/layers/ilayer.cuh

@@ -6,15 +6,6 @@
 
 namespace CUDANet::Layers {
 
-/**
- * @brief Activation functions
- * 
- * SIGMOID: Sigmoid
- * RELU: Rectified Linear Unit
- *
- */
-enum Activation { SIGMOID, RELU, NONE };
-
 /**
  * @brief Padding types
  * 
@@ -85,7 +76,6 @@ class ILayer {
     std::vector<float> weights;
     std::vector<float> biases;
 
-    Layers::Activation activation;
 };
 
 }  // namespace CUDANet::Layers