Stop the search if . is reached
Stop the search if more than one user is returned
In both cases interrupt script and exit

Several options where added including:
--group-size to specify the size of the groups (default 1)
--big-group to attribute remaining emails to the last group
--prefix to add a prefix to all group names

The former one was not working correctly. I shamelessly used one
taken from:
https://uibakery.io/regex-library/email-regex-python

Updated README.md in consequence with a more concrete example as well.

Now the token can be placed in ~/gitedu.token or
in env var $GITEDU_TOKEN or
given to command line with "-t" or "--token" argument

(former "convenient bash script"), close #4

create_group.py and create_repo_for_students.py done

Add optionnal parameters "expires_at" to remove students at date

In create_repo_for_students.py