To keep the distchecks for the documentation, the documentation has to
be built in the check target instead of distcheck-hook.
While at it, rename doc/.build to doc/_build. This naming is the
default with sphinx 0.6.2.
- Add more information to the documentation front page
- Document how to build the documentation
- Clarify the tutorial a bit and remove some quirks
- Bring README.rst up-to-date
- Small enhancements here and there
