area of a marker in mesh
Merge pull request #106 from ppkk/devel

area of a marker in mesh
Work on Shapeset - add L2ShapesetTaylor and polish others.
Fix behavior of linearizer upper bound on levels - take into account the bi-linearity of linear functions on quadrilaterals.
Add MeshFunction<Scalar>::add.
Implement second order Taylor basis.
Add some skeleton of future Postprocessing area of Hermes.
	- implement the VertexBasedLimiter according to Dmitri Kuzmin
Testing of DG limiting.