erc-hide-lines - per channel hide/show

[Corwin Brust]

TL;DR  Appears stable, might try for patches to ERC "soon".

erc-hide-lines - toggle display of IRC message visibility

  https://sr.ht/~mplscorwin/erc-hide-line/

Please test/review & share your feedback!

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I have been using this in my daily driver for around 1yr and I'm happy
with it.  So much so that I will likely offer a patch to see it
included in ERC in the not-too-distant future.  Alternately, this
could go to ELPA (as separate from ERC) -- hence cross-posting to
devel as a sort of Pre-RFC, in case the consensus may be to go that
direction, at least initially. Please share your thoughts if you like
one or the other of these approaches better.

_Recent Updates_

- add ERC module declaration
- easily hide most types using ":most"
- fix inf-loop given invalid settings
- improve README/docstrings

_Less Recent Updates_

- remove need for patching ERC (thanks JP)
- erc-hide-show: (C-h C-h h) set/apply to defaults or channel
- cmd: erc-hide-show-toggle: (C-h M-h) hide/show in current buffer

_Next Steps_

- improve keymap (remove bindings when disabling)
- use erc-track-exclude for (fallback?) defaults
- prep patches to merge to ERC or publish via ELPA

_Later Maybe_

- get hidable types via introspection/code-scraping
- hide stuff per-network, per-nick, combinations, etc.
- support ignore/fools/pals/...?
- extract the "mini-DSL" for ease of reuse
- roadmap supplementing/replacing "drop" based features with
"hide-line" approach

TYVM to many, especially JP for up-to-and hasty drive-by copy-edits of
this note and Emanuel for help getting rid of byte/native comp
warnings, and in advance to the community for your help testing this,
and for your feedback and suggestions.