'Export all modules from `modulestore` and content from `contentstore` as xml to `root_dir`.
`modulestore`: A `ModuleStore` object that is the source of the modules to export
`contentstore`: A `ContentStore` object that is the source of the content to export, can be None
`courselike_key`: The Locator of the Descriptor to export
`root_dir`: The directory to write the exported xml to
`target_dir`: The name of the directory inside `root_dir` to write the content to'

def __init__(self, modulestore, contentstore, courselike_key, root_dir, target_dir):

    self.modulestore = modulestore
    self.contentstore = contentstore
    self.courselike_key = courselike_key
    self.root_dir = root_dir
    self.target_dir = target_dir
