use packing-list consistently

zap old comments that are unlikely to ever come back

thinko
noticed by Bryan Vyhmeister, thx

improve list item formatting;
from salvador sabaini

document what signify2 does, remove remnants of signify/x509.
comment out stuff that's not supported yet, but may make a come-back later

Use .Cm rather than .Ar for fixed strings on the command line
and remove invalid escaping of `@' characters.

allow signing to proceed when interrupted

fix the only .Xr ordering and punctuation issue i could find
with the new MANDOCERR_XR_* warnings in the whole tree

obvious cases of missing .An;
found with the new mandoc(1) MANDOCERR_AN_MISSING warning;
no text changes

no need for .Pp before .It and .Sh, zap trailing whitespace,
and no need to capitalize the first word after a semicolon;
from Jan Stary <hans at stare dot cz>

tweak the way we create and sign packages significantly:

all modern compression formats support multi-stream archives.
Store the packing-list as a separate stream, and note where the
first stream en

tweak the way we create and sign packages significantly:

all modern compression formats support multi-stream archives.
Store the packing-list as a separate stream, and note where the
first stream ends when reading back the packing list.

When pkg_sign sees a split-stream archive, it does not need to unpack/repack
the whole archive: it can just sign the packing-list, close the stream, and
copy the next stream(s) from the source archive verbatim.

This is perfectly transparent to pkg_add, but abuses IO::Uncompress::Gunzip
internals slightly (to be solved with cpan).

also adds explicit option -C for generating a SHA256 list of all packages.

and okay naddy@

show more ...

explain signatures

separate pkg_sign documentation. Option description becomes MUCH saner.