Removed usage of unnecessary `binascii` module in favor of `hexdigest`
Small whitespace fix
Refactored `attachments` attribute from the `HTML` class to an argument for `write_pdf`
Fixed the `default_url_fetcher` for Python 2, which returns a message type with no `get_filename` method
Moved the UTF-8 decoding logic from `compat.py` to `pdf.py`, where it's actually necessary to special case the unquoted result