Silva-app-document

------------------

* ...

------------------

* Update tests to be ran inside a transaction to ensure the last
author is properly set.

------------------

* Extends ``IDocumentDetails`` API:

- Add methods to access the URL of the first image contained in the
document, or its thumbnail.

- Add an option to retrieve the text of the document with downgraded
titles (meaning ``h1`` becomes ``h2``, ``h2`` becomes ``h3`` and so on).

- Add an option to limit the size of the introduction to a given
words (in addition to the possiblity to a given number of characters).

----------------

* Update and import the Silva XML import and export API.

------------------

* Update API to Silva 3.0c1.

* Support automatic edition of the title, like it was done with the
previous ``SilvaDocument`` extension.

* Add a ZMI screen to see the document raw HTML. Improve various API.

* Add a document base class that can be reused by other Silva extensions.

* Fix bugs.

* Improve tests.

------------------

* Initial release.