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

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

Fix bug with limit of 20 first projects forks (see https://docs.gitlab.com/ee/api/README.html#pagination)