Implement backward function for Sub

Context

Implement the backward kernel for Sub operator.

Partially fix #30 (closed)

include/aidge/backend/cpu/operator/SubImpl.hpp

@@ -15,15 +15,23 @@
 #include "aidge/backend/cpu/operator/OperatorImpl.hpp"
 #include "aidge/operator/Sub.hpp"
 #include "aidge/utils/Registrar.hpp"
-#include "aidge/utils/Types.h"
-#include "aidge/backend/cpu/data/GetCPUPtr.h"
-#include <memory>
+
 #include <vector>
 
 namespace Aidge {
 // Operator implementation entry point for the backend
 using SubImpl_cpu = OperatorImpl_cpu<Sub_Op,
-    void(std::vector<std::size_t>, std::vector<std::size_t>, const std::vector<std::size_t>&, const void*, const void*,void*)>;
+    void(std::vector<std::size_t>, std::vector<std::size_t>, const std::vector<std::size_t>&, const void*, const void*,void*),  
+    void(const std::size_t,
+         const std::size_t,
+         const std::size_t,
+         const std::vector<std::size_t>&,
+         const std::vector<std::size_t>&,
+         const std::vector<std::size_t>&,
+         const void*,
+         void*,
+         void*)
+>;
 
 // Implementation entry point registration to Operator
 REGISTRAR(Sub_Op, "cpu", Aidge::SubImpl_cpu::create);