Given the filename, including md5 fragment, construct the
    dependency link for PyPI.

def pypi_link(pkg_filename):
    """
    Given the filename, including md5 fragment, construct the
    dependency link for PyPI.
    """
    root = 'https://files.pythonhosted.org/packages/source'
    name, sep, rest = pkg_filename.partition('-')
    parts = root, name[0], name, pkg_filename
    return '/'.join(parts)