Make (*Client).Sessions() lock-free

add FAIL AUTHENTICATE VERIFICATION_REQUIRED

fix some papercuts

From discussion with @emersion, this will help with UX if people try to
log into their unverified accounts.

Warn about banning a single IPv6 address

Account registrations pending verification should produce a logline and
send a sno.

CS PURGE should send a snomask

Send snomasks for HS SET

OpenSolaris / Illumos Service Management Facility (SMF) Service

Signed-off-by: Georg <georg@lysergic.dev>

NS SUSPEND now req 'ban' capabs

fix two WHO bugs

These should have been committed in 8218d1caab
but weren't.

fix #1833

fix casefolding issue in muting RELAYMSG

update dependencies for 2.9 window

Reported by @mogad0n; the mute mask was being case-canonicalized,
but the RELAYMSG identifier wasn't being case-canonicalized before
the check.

`WHO #channel o` is supposed to return only server operators.
This is RFC1459 cruft; just return an empty list in this case.

RPL_ENDOFWHO should send the original, un-normalized mask

Modernize the list of os-arch pairs that get official release builds;
add darwin/arm64 and openbsd/amd64, remove 386 and armv7, add plan9/amd64
for fun.

The landing page link doesn't seem to work right now.

bump changelog for 2.8.0, fix #1827

Improve documentation for use of certificate fingerprints

Document operator capabilities.

SAMODE +f shouldn't require channel privileges

Reported by @Mikaela; normally this requires +o or higher on the
channel that is the target of the forward, but SAMODE should bypass
this check.

fix error message for NS SET EMAIL without the password

temporary logo update

Languages README.md: Oragono -> Ergo

Signed-off-by: Georg <georg@lysergic.dev>

Thanks @brettgilio!