bug#49860: 28.0.50; add IRCv3 building blocks to ERC

["J.P." <jp@neverwas.me>]

Hi,

I've gone ahead and started laying some groundwork [1]. Although parts
may look rather cemented in place, please don't let that deter anyone
from proposing a new direction, even if that means a complete overhaul.

In the meantime, I'm offering a usable POC-turned-WIP [2] that I'll
continue to update and report on until told otherwise. The basic
approach is rather conservative, with compatibility driving most
decisions. As such, external packages like erc-hl-nicks appear to hold
up just fine, though that's merely a happy side effect. (BTW, I've been
using some form of this as a daily driver for some time now, not that
anyone should care.)

Since waiting for collaborators to emerge from the woodwork may take
forever, I've decided to start shaving off small pieces and submitting
them as separate bugs. Some of these changes won't make much sense
without the larger context, but so be it. And while it may appear like
prevailing attitudes toward bold changes in ERC country would render
such an exercise absurd and quixotic, I think the sheer presence of lots
of little crumbs out on the dance floor leading back here can only help
long term.

Thanks,
J.P.

P.S. Perhaps this bug's severity should be reconsidered because some v3
extensions, like SASL, may soon be de facto required by major networks.


Notes
~~~~~

[1] Latest: https://jpneverwas.gitlab.io/erc-tools/49860/patches.tar.gz
            https://jpneverwas.gitlab.io/erc-tools/49860/logs.tar.gz

    Snapshots for refuseniks:

    https://debbugs.gnu.org/cgi/bugreport.cgi?att=1;msg=6;filename=patches.tar.gz;bug=49860
    https://debbugs.gnu.org/cgi/bugreport.cgi?msg=6;bug=49860;filename=logs.tar.gz;att=2

[2] To try this thing without patching/building, just install as usual:

      (require 'package)

      (push '("erc-tools"
              . "https://jpneverwas.gitlab.io/erc-tools/archive/")
            package-archives)

    Then M-x list-packages RET, and find the bottom-most entry for this
    bug, which should look something like:

      erc 49860.20210805.5 available An Emacs Internet Relay Chat ...

    And hit [Install] in the popup. After that, just add:

      (require 'erc-v3)
      (push 'v3 erc-modules)

      ;; Optionally, add this demo module showing some v3 features in action
      (push 'eldoc erc-modules)

    And connect as you normally would. (If you need SASL, see the
    commentary in erc-v3-sasl.el).