Fix #20
Fix arithmetic of mesh_points in gf

- the arithmetics of the gf mesh_points :
the forwarding of the second argument was missing,
leading to subtle bugs e.g. in  (in matrix case) :

  deltaw(iom_) << iom_ * gw.singularity()(-1) + gw.singularity()(0) - gw(iom_);

because the partial evaluation of the expression introduced a dangling const matrix_view &
instead of moving the temporary matrix_view into the final matrix expression template.
clef : code cleaning

- remove a useless opertor(...)
utility : correct a compile macro

- _j notation was not compiled...
[API change] gf : factories -> constructors

- Make more general constructors for the gf.
  gf( mesh, target_shape_t)
- remove the old make_gf for the basic gf.
- 2 var non generic gf removed.
- clean evaluator
- add tensor_valued
- add a simple vertex test.
- clean specialisation
- Fix bug introduced in 1906dc3
- forgot to resize the gf in new version of operator =
- Fix make_singularity in gf.hpp

- clean resize in operator =

- update h5 read/write for block gf
  - changed a bit the general trait to save *all* the gf.
  - allows a more general specialization, then a correct for blocks

- NOT FINISHED : need to save the block indice for python.
  How to reread ?
  Currently it read the blocks names and reconstitute the mesh from it.
  Is it sufficient ?

- clean block constructors

 - block constructors simplest possible : an int for the number of blocks
 - rest in free factories.
 - fixed the generic constructor from GfType for the regular type :
   only enable iif GfType is ImmutableGreenFunction

- multivar. fix linear index in C, and h5 format

  - linear index now correctly flatten in C mode
    (was in fortran mode), using a simple reverse of the tuple in the folding.
  - fix the h5 read write of the multivar fonctions
   in order to write an array on dimension # variables + dim_target
   i.e. without flattening the indices of the meshes.
   Easier for later data analysis, e.g. in Python.

- merge matrix/tensor_valued. improve factories

  - matrix_valued now = tensor_valued<2>
    (simplifies generic code for h5).
  - factories_one_var -> factories : this is the generic case ...
    only a few specialization, code is simpler.

- clef expression call with rvalue for *this
- generalize matrix_proxy to tensor and clean

 - clean exception catch in tests

  - exception catching catch in need in test
    because the silly OS X does not print anything, just "exception occurred".
    Very convenient for the developer...
  - BUT, one MUST add return 1, or the make test will *pass* !!
  - --> systematically replace the catch by a macro TRIQS_CATCH_AND_ABORT
    which return a non zero error code.
   - exception : curry_and_fourier which does not work at this stage
   (mesh incompatible).

- gf: clean draft of gf 2 times
  - comment the python interface for the moment.
  - rm useless tests
gf: Fix out of bound in linear mesh in gf eval.

- When reaching the last point of the grid,
move one step back and set w =1.
- fix the gf_2times but and related issues.
clean the TRIQS_COMPILER macros

- from now on, C++11 compilers only.
- no ressources to maintain old stuff.
Update documentation

Changelog and some updates were done.
implement array_const_view
arrays: clean dead code
implement gf_const_view
gf/imfreq : remove the little () workaround

- was a bug workaround. Should be ok, but
 reason of previous fix unclear. Suspicious...
- necessary to remove this :
  - it is useless normally.
  - it prevent the evaluator to work for scalar valued gf
gf : various fixes

- blocks : including the iterator
  --> there is still an issue, with the use of & intead of a view
- details after rereading...
gf curry: clean call for a single index

- if the index is not a tuple, make it a tuple...
- better API.
gfs: cleaning code.

Using construction delegation to simplify code.
arrays const_matrix_tensor_proxy delete =
arrays: add rebind const_view from view

- also add some static assert to forbid += and co on const_view
gf: finish block iterator
gf: add rebind view/const + delete swap
gf. Clean code, rereading for doc

- no major change. Code cleaning + clang-format.