[bugfix, doc] enable restructuredText inclusions

This patch is necessary for next pypi upload
- setup.py cannot include files inside restructuredText files.
  Provide a procedure to enable it.
- Update pypi classifiers
- Update HISTORY.rst
- Update CONTENT.rst and pywikibot/CONTENT.rst
- fix some sections in rst-files

Change-Id: Ifc26e40222b0f0c9a86d0b4974954245a12415e0