- rework the coefficients API

- make vectors use a separate loop unroller, so that copying a
row-vector into a col-vector is now possible
- add much more documentation
- misc improvements

doc/examples/class_Column.cpp

@@ -0,0 +1,19 @@
+#include <Eigen/Core.h>
+USING_PART_OF_NAMESPACE_EIGEN
+using namespace std;
+
+template<typename Scalar, typename Derived>
+Eigen::Column<Derived>
+firstColumn(MatrixBase<Scalar, Derived>& m)
+{
+  return m.col(0);
+}
+
+int main(int, char**)
+{
+  Matrix4d m = Matrix4d::identity();
+  cout << firstColumn(m) << endl;
+  firstColumn(m) *= 5;
+  cout << "Now the matrix m is:" << endl << m << endl;
+  return 0;
+}