Avoid manage two versions (html / txt)

Conversion by html2text
Debug : body.txt is no required
Update mails.py
add html2text in travis, MakeFile and tox.ini
test without txt version
debug test
add test without text and without html template
change version to test travis build
Correct Syntax for flake8
Update README.rst
Update README.rst
Raise an error to tell the programmer that something is wrong.
Raise an error to tell the programmer that something is wrong.
Add an example of how to use articles.
Rebase master
Fix requirements + add comments.
Add CONTRIBUTORS.