Added set function.

test/slice.cpp

@@ -19,6 +19,23 @@ int main()
     Matrix<float, 2, 3> B_check(data_check);
     Matrix<float, 2, 3> B(A.slice<2, 3>(1, 0));
     TEST(isEqual(B, B_check));
+
+    float data_2[4] = {
+        11, 12,
+        13, 14
+    };
+
+    Matrix<float, 2, 2> C(data_2);
+    A.set(C, 1, 1);
+
+    float data_2_check[9] = {
+        0, 2, 3,
+        4, 11, 12,
+        7, 13, 14
+    };
+    Matrix<float, 3, 3> D(data_2_check);
+    TEST(isEqual(A, D));
+
     return 0;
 }