- 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_Block.cpp

@@ -0,0 +1,23 @@
+#include <Eigen/Core.h>
+USING_PART_OF_NAMESPACE_EIGEN
+using namespace std;
+
+template<typename Scalar, typename Derived>
+Eigen::Block<Derived, 2, 2>
+topLeft2x2Corner(MatrixBase<Scalar, Derived>& m)
+{
+  return Eigen::Block<Derived, 2, 2>(m.ref(), 0, 0);
+  // note: tempting as it is, writing "m.block<2,2>(0,0)" here
+  // causes a compile error with g++ 4.2, apparently due to
+  // g++ getting confused by the many template types and
+  // template arguments involved.
+}
+
+int main(int, char**)
+{
+  Matrix3d m = Matrix3d::identity();
+  cout << topLeft2x2Corner(m) << endl;
+  topLeft2x2Corner(m) *= 2;
+  cout << "Now the matrix m is:" << endl << m << endl;
+  return 0;
+}