Sphinx based docs and rtd documentation

The documentation contains contents from the README broken up into multiple pages and an API docs section that is autogenerated from the sources' docstrings.  Some minor modifications have been made w.r.t. links beetween the doc pages.

The result is available here: https://confab.readthedocs.org/en/latest/.  Documentation is rebuilt on every push to the Github repository, currently set to my feature branch https://github.com/disko/confab/tree/feature/sphinx_and_rtd_documentation.  I'll happily switch to your master branch once the PR is merged and add you as a maintainer on the RTD project as soon as I know your RTD user name.

Hope you like it!