grammar (typo)

Especially with regard to write capacity and search.

This hasn't been updated in a while and I feel that it is out of date.

I feel that this could use more work, but I'm anxious to do an
incremental improvement given the screencast I just released. :)

We need a newer setuptools on older versions of Python to be able to install recent Sphinx because of its use of environment markers.

Also add note on supported versions to the docs and readme.
Fixes #168.

Update tox.ini to correctly run testdocumentation and DRY with test deps.

- can ``make html`` from doc directory and get html.

- documentation tests run as part of normal tests.

README.rst needs some love.

Then on to making this work with RTD.

Fix broken link (https://bugs.launchpad.net/zodb/+bug/1287046)

- Add missing files from last checkins.

Include the overview in the documentation TOC and move the former link into
the "and more" conclusion.