Python's enums are not extensible, values can't be added and they can't
be subclassed. This is problematic if weboob devel adds new values,
because stable weboob will not be able to use them. They would need to
be replaced by a default value or None, which loses information.

Instead, implement custom enums that contain plain constants and support
adding values aftewards.

a5989d14 renamed README, but references
to it should also be updated.

As of writing, debian stable (stretch) uses Pillow for PIL.

Deprecate html2text<3.200 and add it to requirements.
This is a light dependency and it is used by a great number of modules.

The syntax for using a metaclass is different in python2 and python3,
and there are existing helpers.

Add six as a dependency in setup.py.

hydrargyrum authored Mar 03, 2016 and Romain Bignon committed Jan 28, 2017

QGalleroob allows to search galleries and images and browse collections
of those.

There should not be an an __init__.py in the modules/ directory.
But in case it gets added, the change in setup.py will prevent
installation.

We don't support python 2.6 anymore

It's used on many modules, add it to the base of requirements

--requires is not it; see
https://mail.python.org/pipermail/distutils-sig/2013-December/023180.html

This should help end-users to install weboob on their systems.

closes #929