Introducing sphinx doc

[benoitbryon]

Changelog overview:

• introduced Sphinx documentation in docs/ folder.
• introduced zc.buildout to install Sphinx (and other development tools). See docs/dev/install.txt
• moved content from README.rst to docs/ folder.

Notes:

• @Natim: I didn't set your website or email address in docs/AUTHORS.txt... choose the one you want to appear
• didn't set the license.
• used .txt extension for restructured text files:
  • we can create links to lines here in Github. As an example, we can do this https://github.com/benoitbryon/Thumbnailer/blob/introducing-sphinx-doc/docs/engines.txt#L25 but not that https://github.com/benoitbryon/Thumbnailer/blob/introducing-sphinx-doc/README.rst#L12
  • some directives (like code-block) are not parsed by rst2html (Github's parser for .rst files). It means that sphinx's "make html" output differs from Github's rst2html one. Sphinx should be the reference.
  • if the project survives then the HTML documentation reference will be on readthedocs or packages.python.org but not github. I mean there will be no need to have a HTML doc here at Github.