add file organizer to organizer files in separate assets folder

[sunz1e]

based on @aahnik 's script
https://gist.github.com/aahnik/2c18af0ee937bb2947873774f069adc4

Thanks @aahnik 🙂

Additions:
added utf8: I hope it should fix UnicodeDecodeError which @jamesdeluk faced
use os.path.sep instead of hardcoded separator: I hope it should run on windows as well now.

fixes #36
@leoncvlt

[yokharian]

I think it was easier to change the cache_file function of notionparser.py and extend the self.dist_folder variable since now there is no cache the program always does a download despite the file existing
in addition to the fact that the HTML tags do not refer to the new address, there has to be some kind of configuration on the server to redirect links with png extensions to the path /assets/sep/images/ which is not compatible with all static site providers, for example github pages I did not find it anywhere that supports this configuration.