Refs #77. Added package_part property
Refs #77. Updated test case since we are technically ignoring namespaces
Refs #77. Added hyperlink support
Refs #77. Removed obsoleted code
Refs #77. Should be using KeyError instead of IndexError
Refs #77. Loop through the relationships instead of just adding the first one
Refs #77. Return the created part, since we can
Refs #77. If path is explicitly None, just early return
Refs #77. Updated base test case to use the new classes
Refs #77. Import ZipFile from utils
Refs #77. Use the package_part property
Refs #77. Catch the KeyError, the function does not return None