Migrate output layer

src/backends/cuda/layers/output.cu

@@ -0,0 +1,14 @@
+#include "output.hpp"
+
+#include "cuda_helper.cuh"
+
+using namespace CUDANet::Layers;
+
+float* Output::forwardCUDA(const float* input) {
+    CUDA_CHECK(cudaMemcpy(
+        h_output, input, sizeof(float) * inputSize, cudaMemcpyDeviceToHost
+    ));
+    CUDA_CHECK(cudaDeviceSynchronize());
+
+    return h_output;
+}