Reorder pg_ctl promote after pg_ctl status

Since start/stop/restart/reload/status is a kind of standard command
set, it seems odd to insert the special-purpose "promote" in between
the closely related "restart" and "reload".  So put it after "status"
in code and documentation.

Put the documentation of the -U option in some sensible place.

Rewrite the synopsis sentence in help and documentation to make it
less of a growing mouthful.