editrc(5): Markup fixes

Include EDITRC in doc.

documentation improvements (Ingo Schwarze)

new man page from Ingo Schwarze.

Remove empty callbacks (Ingo Schwartze)

Bump date for previous.

From Ingo Schwarze, based on changes from Kaspars Bankovskis:
* Document error handling of el_init(), el_set(), el_source(),
and history_init().
* Fix a typo an improve punctuation below H_SETUN

From Ingo Schwarze, based on changes from Kaspars Bankovskis:
* Document error handling of el_init(), el_set(), el_source(),
and history_init().
* Fix a typo an improve punctuation below H_SETUNIQUE.
* The ellipsis already implies "optional", no need for [].
* Sort options in editrc(5).
* Prevent e.g. rom being misconstrued as the end of a sentence.
* Drop a useless duplicate .Ar macro.
* Put telltc in its proper place in the alphabetical order.
* A few typos in vi editor command names.
* Some missing vi editor command names.
* Some missing author macros.

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Add FILES section.
From jmc@OpenBSD.

Switch from Op to Oo/Oc for nested block.

Markup consistency, from YOMURA Masanori. Add serial comma.

Drop trailing whitespace.

Don't use .Xo/.Xc to work around ancient macro argument limit in groff.

Fix preamble to match order set out by mdoc(7). Discussed with wiz.

Convert TNF licenses to new 2 clause variant

Change to a 3 clause copyright after permission of the holders.

Document history builtin commands.

Bump date for previous.

Allow setty to set chars using char=value

Add Ns.

setup -> set up, from jmc@openbsd.

em-gosmacs-traspose->em-gosmacs-transpose (Igor Sobrado, PR misc/19909)

empty, not emptry. By Adrian Mrva.

Punctuation nits.

`existent', not `existant'

improve description of line syntax