Implement norm2 in a more efficient way using inner() with some optimisation,see #223
split feelvf/products.hpp into inner.hpp (implements inner()) and cross.hpp
(implements cross()), see #226
added tests for inner/norm2 in testsuite/feelvf
Merge branch 'develop' of https://github.com/feelpp/feelpp into develop
@asamake NO_MPI_TEST for test_wire_basket
implemented mortar method in 2D #36 into the language (works ok for P1 as
soons as integrate on internal elements and boundary elements on the test
function mesh is done separately), see test_mortar.cpp
there are a lot of non-optimal/redundant big changes (copy/paste for mortar
case), 
there are still issues with higher order
Merge branch 'develop' of https://github.com/feelpp/feelpp into develop
Merge branch 'develop' into feature/explicit