Only fetch posts that where made after the day the beerblogging first bet started: 21/03/2011
But would be better if could set in each member the date that he/she entered the site, maybe even automaticaly using some post receive hooks(don't know if github has something for this)?
refs #13
Now each member has it own date_joined in the yaml file.
refs #13
Adding the reset_db method, this should be runned to put in pratice the new fetch post logic, that ignores the post made before
the date_joined from each member.
If the db is not reseted then the old post will still be there =/
can use the cmd like:

    ./manage.py reset_db

and then fetch the posts again:

    ./update_posts.sh

fix #13