[doc] minor operator changes, wien2triqs --> dft_tools
[utility] Add bisect function

* Fixes some problems with the dichotomy function, I believe it to be quicker too.
[gfs] Fix a bug in Fourier transforms

With time points both at the beginning and at the end one must be careful
to manually reweight the first point in the time sum and add the last
point in order to make sure no symmetry gets broken. Added a simple test.
[gfs] Add a python test for slicing
Fix #167
Fix hdf5 formats

- h5 : Python :
- h5 : C++ : add options 'w', 'r', 'a' for C++ file constructor
  to mimic Python
- block gf : clean the hdf5 format and save/load difference between
  Python and C++
- rewrite gf_base_op test to eliminate the h5 file (big).