update : .gitignore

Look who's glooming through? Wait some more commits and PRs ...
update : Gemfile

See, a Jekyll project is nothing without Jekyll.
update : feed.xml

The originally used template produced a nasty, non-important warning.
Resolved thanks to http://michaellee.co/jekyll-layout-build-warnings/
update : download_avatars.py : with Shebang environment

For easier and quicker running without having to type the whole `python` word all of the time.
Merge pull request #242 from hackers4peace/feature/techstuff

3. Technical Improvements