Add lambda wrapper from exercise 3

include/lambda_wrapper.h

+#ifndef __LAMBDA_WRAPPER_H__
+#define __LAMBDA_WRAPPER_H__
+
+#include <cassert>
+#include <vector>
+
+#include <cmath>
+#include <cstdint>
+#include <iostream>
+#include "function.h"
+#include <functional>
+
+namespace numerics {
+
+	template <typename argtype, typename valtype>
+	class LambdaWrapper : public Function<argtype, valtype> {
+	public:
+		LambdaWrapper(std::function<valtype(argtype)> func, size_t indim, size_t outdim) : input_dim(indim), output_dim(outdim), f(func) {}
+
+		virtual valtype operator()(argtype arg) const override {
+			return f(arg);
+		};
+
+		virtual size_t input_dimension() const override {
+			return input_dim;
+		}
+
+		virtual size_t output_dimension() const override {
+			return output_dim;
+		}
+	protected:
+		size_t input_dim, output_dim;
+		std::function < valtype(argtype)> f;
+	};
+
+}; // namespace numerics
+
+#endif