change web server to gunicorn

* run.py doesn't launch the webserver in subprocess anymore
* gunicorn is now used as webserver
* supervisor is used to ... supervise all the process
* added supervisord.conf
* README updated to reflect changes
added update script in supervisord.conf

+ update script now updated to work with new user.txt and htag.txt
method to change port updated to match gunicorn use
supervisor description modified
server url not hardcoded anymore
default port for twitter-rss will stay 5000
support user/htag alone in user.txt/htag.txt
regex rewrited
typo
precision in readme