delta: Fix broken separator support

systemd-delta man page promises that multiple types of deltas will be
concatenated if they are listed with a comma as separator.  Replace
FOREACH_WORD() with FOREACH_WORD_SEPARATOR() to restore the functionality.
terminal/screen: fix GL/GR double-mapping

We must not call screen_map() multiple times for the same input char. Fix
the double-mapping for GL/GR maps are correctly applied.
man: add a link to systemd-coredump(8) in Description of coredump.conf(5)
man: fix link to systemd-networkd-wait-online.service in systemd-networkd.service(8)
man: document equivalence between Limit directives and ulimit

See https://bugs.freedesktop.org/show_bug.cgi?id=80341
man: fix typos
man: document that we set both soft and hard limits for Limit directives

See
http://cgit.freedesktop.org/systemd/systemd/tree/src/core/load-fragment.c#n1100
journald: close passed fds we cannot make sense of

This is mostly likely the audit socket, and we really should close it
if we cannot make sense of it, since as long as it is open the kernel
might disable the kmsg forwarding of audit msgs, and we should avoid
that, since audit msgs might get completely lost then.

I also downgraded the log message we show a bit, after all things should
really work fine, and we proceed fine with it.
timesyncd: minor simplification
cgroup-util: Don't send SIGCONT after SIGKILL
update TODO
When warning about unsupported options, be more detailed
core: warn and ignore SysVStartPriority=

Option was being parsed but not used for anything.
update TODO
resolved: make TXT RR generation and parsing more in-line with RFC 6763, section 6.1

The RFC says to encode an single empty TXT string instead of an empty
TXT array. It also says to treat a zero-length TXT RR as a TXT array
with a single zero-length string.