Started Loss, done softmax, up to p.125

I've implemented alot of support functions that needs to be refactored, optimised and tested; mean.h, exponential.h, matdiv.h matsum.h matsubtract.h. Maybe we need to have a look at if matdiv/matmul should be in the same. Same with matadd/matsubtract and if some of it should be in matvec.h.

include/numerics/mean.h

@@ -0,0 +1,31 @@
+#ifndef _mean_n_
+#define _mean_n_
+
+#include "./utils/vector.h"
+#include "./utils/matrix.h"
+#include "./core/omp_config.h"
+
+namespace numerics{
+	
+	template <typename T>
+	T mean(utils::Vector<T>& A) {
+
+		T mean(T{0});
+	    
+	    const uint64_t rows = A.rows();
+	    const uint64_t cols = A.cols();
+
+
+	    for (uint64_t i = 0; i < cols; ++i) {
+	        for (uint64_t j = 0; j < rows; ++j) {
+	            mean += A(j, i);
+	        }
+	    }
+	    mean /= (static_cast<T>(rows)* static_cast<T>(cols));
+	    return mean;
+	}
+
+
+} // namespace numerics
+
+#endif // _mean_n_