doc: added info on Cython for installation
doc: added a warning for cython version on ubuntu
doc: reorganized files according to new doc structure [in progress]
Set CMakeLists for documentation

The documentation compiles fine. The cosmetics still needs to be done
but at this stage one can work on writing documentation.

  modified:   cmake/BuildSphinx.cmake
  new file:   doc/_templates/index.html
  new file:   doc/_templates/layout.html
  new file:   doc/conf.py.in
  new file:   doc/contents.rst
  modified:   doc/CMakeLists.txt
  modified:   doc/reference/python/data_analysis/fit/fit.rst
  modified:   doc/reference/python/data_analysis/plotting/plotting.rst
  modified:   doc/reference/python/green/block/GfImFreq.rst
  modified:   doc/reference/python/green/block/GfImTime.rst
  modified:   doc/reference/python/green/block/GfLegendre.rst
  modified:   doc/reference/python/green/block/GfReFreq.rst
  modified:   doc/reference/python/green/block/GfReTime.rst
  modified:   doc/reference/python/green/transforms.rst
  modified:   doc/reference/python/green/tutorial.rst
  modified:   doc/tutorials/applications/solvers/aim.rst
  modified:   doc/tutorials/applications/solvers/dmft/dmft.rst
  modified:   doc/tutorials/applications/solvers/settingparameters.rst
  modified:   doc/tutorials/python/tour1.rst
added overview and python execution in doc
updated installation instructions for Mac OS X
doc: putting toc back

- to be improved