Use release_urls() XMLRPC method for the time being
Use release_urls() XMLRPC method for the time being

This replaces the `package_urls()` XMLRPC method by the `release_urls()`
method, since the former was deprecated and no longer works. Invoking the
endpoint results in an error:

    This API has been deprecated. Use https://pypi.org/xxx/yyy/json instead.
    The XMLRPC method release_urls can be used in the interim, but will be
    deprecated in the future.

This addresses issue #95. However, this is only a quick-fix, since the
`package_urls()` method will also be deprecated in the future.

saschpe/py2pack