fix feed.xml is not included in pypi's package

fix feed.xml is not included in pypi's package, while run "python setup.py sdist"

in pypi's dowload package: https://pypi.python.org/pypi/rutherford/0.7

It is not include the feed.xml, because setup.py "Installing Package Data" miss a config

see also: https://docs.python.org/2.6/distutils/setupscript.html#installing-package-data