update hoauth2 to check membership (github return a response status = 204 instead of 200)
added a query to check membership in an organisation, provided an option github-org is given in github section of configuration
removed github name and use login instead as it is not always present in the github response, added read:org scope depending on whether it is set in the configuration file
default.conf: added commented dummy github org
authentication error trigger a log WARNING instead of an error
README updated: github organization membership