Replaced `urlopen_contenttype` with `urllib_get_content_type`, `urllib_get_charset` and `urllib_get_filename`.
Moved `temp_directory` to `testing_utils` to allow reuse in other test files.
Use `temp_directory` in favor of `tempfile` in the PDF embedded files testcase.
Fix parsing of <link rel>
Use the new `element_has_link_type` instead of parsing the `rel` attribute manually.
Renamed `is_internal` to `link_type`, which is less confusing