NS SAREGISTER should send machine-readable responses. A simple approach:
check if the account-registration cap is enabled, and if so, send the
the same responses that would be sent by the REGISTER command.

Add more clarify in NS INFO and SAREGISTER about unregistered nicknames

Fixes #1924

See discussion on #1891

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

Improve documentation for use of certificate fingerprints

See #1676

* Add email-based password reset

Fixes #734

* rename SETPASS to RESETPASS

* review fixes

* abuse mitigations

* SENDPASS and RESETPASS should both touch the client login throttle
* Produce a logline and a sno on SENDPASS (since it actually sends an email)

* don't re-retrieve the settings value

* add email confirmation for NS SET EMAIL

* smtp: if require-tls is disabled, don't validate server cert

* review fixes

* remove cooldown for NS SET EMAIL

If you accidentally set the wrong address, the cooldown would prevent you
from fixing your mistake. Since we touch the registration throttle anyway,
this shouldn't present more of an abuse concern than registration itself.

"LOGOUT ALL" logs out all clients for a user.

Fixes #1712.

See #1659

Fix error message for privileged NS PASSWD on a nonexistent account

Users logged into an account can see their own email.
Opers with the accreg capability can see all users.

Fix incorrect description of channel ownership in NS INFO

Warn users that NS UNREGISTER doesn't give them a "do-over";
the account name will remain reserved.

CS INFO with no arguments should list your registered channels

List IRCv3 CAPs in `NS CLIENTS LIST` output

PerstentStatusMandatory should display as "enabled", not "mandatory",
in the context where it refers to a user-chosen setting.

make PASSWORD an alias for PASSWD in nickserv

Improve auditability of sensitive operator actions

strip local_ from oper capab names, also consolidate unban into ban

Fixes #1380

Enhancements to NS SUSPEND, including stored metadata and the ability
to list suspensions

CLIENTS LIST shows information about clients attached to a nick.
CLIENTS LOGOUT allows individual (or all) sessions to be logged out.

SESSIONS is now an alias for CLIENTS LIST.

Fixes #1072.