don't AppVeyor with failure on Py3, too slow
Auto rst generated docs with custom index.rst
docs/generate_rst.py for generating rst files
make generate_rst.py executable
only generate menpo docs if __name__ == '__main__'

So we can re-use this code for menpofit/menpodetect etc
Merge pull request #525 from jabooth/docfixes

Fix .rst doc files, auto-generation script