Modernize pyrnotify

[JulienPalard]

Script info

• Script name:  pyrnotify
• Version: 2.0

Description

As a new user of pyrnotify I proofreaded the code before using it and fixed a few things, sorted by importance (most important first):

• Fixed a bug where only 1k notifications can be handled due to the 'accept' being called recursively and the Python stack limit being 1k calls by default.
• Starting a line with a dash, then mentioning me, like -w mdk was crashing notify-send with the Option inconnue -w mdk message (Unknown option -w mdk).
• Fixed a potential bug in TCP recv code: received bytes were UTF-8 decoded by chunks instead of decoded as a whole, so if a chunk were cutting on a multibyte UTF-8 char both decodes (before and after the cut) would fail. I bet this never occur in practice because message were never truncated (a single TCP packet should always be enough for a notification?).
• The re.sub(r'([\\"\'])', r'\\\1', s) to serialize arguments in a shell-like form was hurting my eyes, both from a security and from a readability point of view. I did not attempted to exploit it though, maybe it's safe, it just calls to be exploited. I replaced "shell-like-serialization" with json, so we don't have to care about quotes, the json module does.
• I removed old Python 2 compatibility.
• I ran black on the code.

I did this "in the rush" to test it for myself, outside the git repo, I'm very sorry it's a single big ugly commit, if needed I'm OK to split this cleanly for easier code review.

Checklist (script update)

• Author has been contacted
• Single commit, single file added
• Commit message format: script_name.py X.Y: …
• Script version and Changelog have been updated
• For Python script: works with Python 3 (Python 2 support is optional)
• Score 100 / 100 displayed by weechat-script-lint

[flashcode]

Thanks, merged!

With minor changes: tabs removed in comments, fixed a typo in comment.