Fix for C++11 and gcc 4.8
[doc] update compiler requirements.
[cmake] Add USE_CPP14 is TRIQS_Config

- for usage in applications
[gfs] Change bz tag to using the actual brillouin_zone class

- simpler to remember ...
- in this case, gf is specialized on the actual name of the domain.
[gfs] Various fixes, for paper
Correction
fix C++11 issue in clef
API change in mpi: rename allreduce -> all_reduce
[doc] Install on Ubuntu 14.04
[mpi] Work on draft

- add invoke2, works now for block_gf
- TODO: more systematic tests
- TODO: remove the mpi.hpp, include as higher heder like in gf
Fix previous commit for c++11
Fix hdf5 formats

- block gf : clean the hdf5 format
- doc