Added Block Operations tutorial and code examples

doc/examples/Tutorial_BlockOperations_corner.cpp

@@ -0,0 +1,27 @@
+#include <Eigen/Dense>
+#include <iostream>
+
+using namespace std;
+using namespace Eigen;
+
+int main()
+{
+  MatrixXf m(4,4);
+  
+  m << 1, 2, 3, 4,
+       5, 6, 7, 8,
+       9, 10,11,12,
+       13,14,15,16;
+
+  //print first two columns
+  cout << "-- leftCols(2) --" << endl
+    << m.leftCols(2) << endl << endl;
+  
+  //print last two rows
+  cout << "-- bottomRows(2) --" << endl
+    << m.bottomRows(2) << endl << endl;
+    
+  //print top-left 2x3 corner
+  cout << "-- topLeftCorner(2,3) --" << endl
+    << m.topLeftCorner(2,3) << endl;
+}