Add some more examples for the API documentation.

The only missing examples now are for homogeneous() and hnormalized();
I don't know what they're used for ...

doc/examples/MatrixBase_cwise_const.cpp

@@ -0,0 +1,18 @@
+#define EIGEN2_SUPPORT
+#include <Eigen/Core>
+#include <iostream>
+
+using namespace Eigen;
+using namespace std;
+
+int main()
+{
+  Matrix3i m = Matrix3i::Random();
+  cout << "Here is the matrix m:" << endl << m << endl;
+  Matrix3i n = Matrix3i::Random();
+  cout << "And here is the matrix n:" << endl << n << endl;
+  cout << "The coefficient-wise product of m and n is:" << endl;
+  cout << m.cwise() * n << endl;
+  cout << "Taking the cube of the coefficients of m yields:" << endl;
+  cout << m.cwise().pow(3) << endl;
+}