Fix CMakeLists so that Python package only depends on the Sphinx documentation (not on the Doxygen documentation).
Review and update documentation introduction.
Review and update 'viennagrid.wrapper' tutorial.
Review and update compilation instructions.
Review and update API reference, and make fixes in the high-level module.
Write short developer's guide.
Add information on how to run the tests for the wrapper using CMake.
Update project README.
Write 'viennagrid' tutorial.
Change index depth to 2.
Change CMakeLists to also generate Sphinx documentation as LaTeX.
Merge branch 'doc' into devel