Incorporate new finite element methods in GetFEM++

Basically, It is sufficient to describe an element on the reference element, i.e. to describe each base function of each degree of freedom. Intrinsically vectorial elements are supported (see for instance Nedelec and Raviart-Thomas elements). Finite element methods that are not equivalent via the geometric transformation (not -equivalent in GetFEM++ jargon, such as vectorial elements, Hermite elements ...) an additional linear transformation of the degrees of freedom depending on the real element should be described (see the implementation of Argyris element for instance).

Please read Description of the Project for more details and see the files getfem/getfem_fem.h, getfem_fem.cc for practical implementation.