Added slice function for matrix.

test/slice.cpp

@@ -0,0 +1,25 @@
+#include <stdio.h>
+
+#include <matrix/math.hpp>
+#include "test_macros.hpp"
+
+using namespace matrix;
+
+int main()
+{
+    float data[9] = {0, 2, 3,
+                     4, 5, 6,
+                     7, 8, 10
+                    };
+    float data_check[6] = {
+        4, 5, 6,
+        7, 8, 10
+    };
+    SquareMatrix<float, 3> A(data);
+    Matrix<float, 2, 3> B_check(data_check);
+    Matrix<float, 2, 3> B(A.slice<2, 3>(1, 0));
+    TEST(isEqual(B, B_check));
+    return 0;
+}
+
+/* vim: set et fenc=utf-8 ff=unix sts=0 sw=4 ts=4 : */