new versions available, this resolves conflicts
Replaced uwsgi with gunicorn (reason: downloads were not reliable with uwsgi)

gunicorn is built by buildout and has one external dependency: libevent
there is a configuration file, gunicorn_settings.py.
Command to run gunicorn: bin/gunicorn -c gunicorn_settings.py wsgi:application
remove potential issue with too many open file pointers for large downloads
updated documentation with new dependencies
added ext dependency to travis.yml