- 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/snippets/MatrixBase_dynBlock.cpp

@@ -1,3 +1,3 @@
-Matrix4d m = Matrix4d::identity();
-m.dynBlock(2,0,2,2) = m.dynBlock(0,0,2,2);
+Matrix3d m = Matrix3d::diagonal(Vector3d(1,2,3));
+m.dynBlock(1, 0, 2, 1) = m.dynBlock(1, 1, 2, 1);
 cout << m << endl;