start working on #369
 - provide access to face dof similar to element dof
 - introduce FaceDof as a subclass of tuple to ensure backward
 compatibility. this allows to have a more readable interface
up #369 for Lagrange finite element
 - implement local interpolant
 - implement local face interpolant
up #369
 - use local interpolant framework  and hence provide global interpolant
thanks to the doftable
up #369
 - cleanup
up #369
 - provide geometric mapping data structure in Expr class to facilitate access
 to it when computing the local interpolant
up #369
 - fix compilation
up #369 and #251
 - implement l2 projection
up #369 test with local interpolant
up submodule
up #369: cleanup and fix compilation
up #369
 - implement project on face in on()
 - use local face interpolant
revert to initial code
fix compilation
access to geometric mapping properly
up #369 and #252
 - implement local interpolant (not working yet)
up #369 and #252 use local interpolant
up #369 fix global interpolant (need some more work)
up #369 fix compilation in composite case
up ChangeLog [ci skip]
merge