rename directory to eikonal
@feelpp/feelpp 
added functions section to provide readily available coefficient functions for
example such that the user does not have to define them

see doc/manual/advectoin/dar_gals.{cpp,cfg} for an example
@feelpp/feelpp, feelpp/rb4areao

add diffusion advection reaction example
Merge branch 'develop' of https://github.com/feelpp/feelpp into develop
@feelpp/feelpp, @feelpp/rb4areo

 - added functions.f
 - added GaLS stabilisation terms

to test try 

feelpp_dar_gals --functions.epsilon=1e-5 --functions.delta=0

the first parameter make the convection dominant and the second cancel the
stabilisation terms, you will see the instabilities, the results are wrong

then try : 

feelpp_dar_gals --functions.epsilon=1e-5 --functions.delta=1

and see the effect of the GaLS stabilisation terms
@feelpp/rb4areo 
added to CMakeList.txt and renamed