Dataflake-docbuilder

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- Feature: Added a script and buildout option ``index-name`` to
specify the file name (without extension) for the index page.
With this option you can safely build the index page into an
existing `Sphinx` documentation folder without overwriting
or changing the existing ``index.rst`` file and its HTML
equivalent. The default continues to be ``index.rst``, though.

- Feature removed: It is no longer possible to create a simple HTML
index page without using `Sphinx` and a minimal `Sphinx`
configuration.

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- Feature: Add new script option ``-g``/``--grouping`` and zc.buildout
option ``grouping`` to group packages.

- Miscellaneous: Renamed the zc.buildout option `source` to `sources`
since it contains one or more elements.

- Miscellaneous: Removed the version pinning on the Sphinx dependency
since our other dependency (repoze.sphinx.autointerface) is now
compatible with Sphinx 1.0.

- Bug: If pkg_resources.find_distributions cannot find valid
Egg distributions we still force the tag folder itself into the
pkg_resources.working_set as a fallback.

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- Feature: The user can now provide a Sphinx configuration folder
path that will be used to generate additional content for the
documentation root folder.

- Factoring: Moved the DocsBuilder class into its own module.

- Factoring: Save run state on the documentation builder class
instead of handing it around

- Cosmetic: Use a flat hierarchy when creating the HTML output links
instead of a folder per package. Only a single index page needs to
be created that way.

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- Initial release