[exceptions] Add mpi node number and C++ trace to C++ exceptions.

- Trace : to be decided if we keep it -> or put it in the python object.
Revert "Modify det_manip to access determinant x_values and y_values"

This reverts commit d8e79056bffc13598ca63305610c5edd2182c21f.

After all, these functions are not useful...
[arrays] Add frobenius_norm to the lib.

-TODO : add the test !
-from cthyb project.
- change the name of the file
Add macro TRIQS_WRAP_ARG_AS_DICT for python parameter wrap

- Rename the attribute((annotate(...))
  because i) it is clearer ii) it leads to a warning on gcc.
Correct 0c34877b9babdd07f5a6e99ed172b967124b7e8e

- The char * was dangling ..
- add TRIQS_EXCEPTION_SHOW_CPP_TRACE
  if defined, the C++ trace will be added to the error message.
  Mainly for debug purpose only, it is disturbing for normal usage,
  since it leads people to believe the code has crashed...
added includes in gfs header
Fix #142. boost serialization of matsubara_freq_mesh.

boost serialization of matsubara_freq_mesh was broken
by the introduction of the window for the MPI api...
Added test for statistics + fix bug variance

This is the basic example of the paper.
Also fixed a strange problem in computation of the variance:

I have identified cases where:

$$ 1/N sum_i (x_i- m)^2  \neq 1/N sum_i x_i^2 - m^2 $$

with $ m = 1/N sum_i x_i $

In particular, the RHS (which corresponds to previous implementation) may give **negative** variances!! LHS seems to be more accurate (especially in cases where x_i is very close to m) --> changed implementation to LHS
[doc] update to preliminary introduction, prettification
[doc] Fixed example #99
[doc] stated faqs.rst with text file printing info
[doc] faq: added more about text file saving
rm parameter class, fix #124

- now replaced by simpler and better code generation solution
- TODO: write the documentation, implemented for cthyb solver
[wrapper] Split the converters code, fix #121 and hello_world

- The wrapper_tools.hpp is split into several converters/xxx.hpp
- to include only on demand.
- This fixes the hello_world from the paper
Fix #145 : Compilation on Ubuntu 14.04 32 bits

- one integer type was wrong
- detection of python : patch is different for 32 bits than the usual path in 64 bits.
Fix #152
[gfs] Fix out of bound error in fit_tail

- n_max must be checked against max size of mesh
  or bad input in python will lead to undefined behaviour,
  random results and valgrind error....

- At this stage, I leave the ENFORCE_CHECK macro in fit_tail.cpp
  for checks.
  TO BE REMOVED when code is reviewed.
Silence some gcc warnings.
[gfs] Opt->Evaluator.  Rework evaluator for multivar gf

- fix on_mesh :
   method can be called with mesh_point
   on_mesh wrapper class can be called with lazy arguments.

- add make_regular function to fix sum
  - make_regular (x) -> return a regular copy, forcing the evaluation of expression templates.
  - TODO : do it for array_expr, gf_expr

- mesh product: index_t as a class
  to permit construction from a tuple of mesh points to components

- Opt -> Evaluator
  - Opt template param is replace by Evaluator
  - Evaluator : default is void, (default evaluator as before)
  - allows to add a custom evaluator (cf new test sym3).

- Change evaluator concept
  - Now evaluator must have one constructor taking (G* g)
    with the gf, given at construction.
  - Allow to prepare some data.
  - E.g. sym3
[gfs] Test mpi for multivar gf.

TODO : more test.