replace docpot with docopt-ng

[sudoskys]

Thanks for your work!

I have imported sumy as text summarization tool in this repo

https://github.com/sudoskys/llm-kira

but I found that the docopt of this repo was no longer maintained and cause some issues here
lss233/chatgpt-mirai-qq-bot#62 (comment).

Details can be found here
docopt/docopt#502.

Therefore, I suggest the use of https://github.com/jazzband/docopt-ng to replace docopt.

[miso-belica]

Hi @sudoskys, thank you for pointing this out. It is sad @keleshev is not responding anymore. I was a big fan of his projects. Are you willing to send a PR for replacing docopt?

[sudoskys]

I will have a try!

[miso-belica]

Fixed in #191