input: don't quit with exit status 1 when receiving SIGTERM

Instead, do whatever the normal "quit" command does, which currently
is returning a status of 0.
mp_msg: define a bunch of convenience macros

In order to use bare mp_log contexts, I find myself creating dummy
structs (with a single "log" field) to use the MP_ERR() etc. macros,
which hardcode the idiom that a context struct has a log field. On the
other hand, just using mp_msg_log() is too much typing (and I want to
rename it to mp_msg() when the transition is done), so it seems nice to
have message printing macros that use mp_log directly.
input: avoid using wakeup pipe if it's not needed

If input is not waiting for select(), writing to the wakeup pipe is
wasteful, and, if there are many wakeups, might even block the wakeup
threads if the pipe gets full.

However, if it's waiting for select(), the wakup pipe must be used to
unblock the waiting thread. Actually there's a small race condition: we
might determine that the main thread is in select(), and write to the
wakeup pipe (whether we do this while unlocked or locked doesn't really
matter). Then, the main thread might leave select() before reading from
the wakup pipe. This should be harmless, because at worst more wakeups
than needed happen, but never fewer.
manpage: undocument syntax for skipping optional arguments in input commands

"-" could skip optional arguments. I think this was a pretty bad idea,
because it introduced a weird special case.

I'll remove the special syntax, but keep compatibility for the "seek"
and "screenshot" commands.
input: remove weird syntax for skipping optional arguments
input: move some command flags into a bitfield
input: better error reporting for missing commands

Don't print an empty string if the command is missing.
input: adjust code to make quoted/not quoted cases more unified
input: move multi-command parsing somewhere else

I'm planning to add a mode to pass commands as a pre-split list of
strings, and this will probably be useful to reach this goal.
manpage: fix --vf=expand aspect ratio example
command: scale osd’s time remaining by the current speed

Signed-off-by: wm4 <wm4@nowhere>
command: mess with previous commit

Nothing actually used the returned length. Since the remaining time can
easily become 0 or negative (e.g. incorrectly estimated file duration),
the time_remaining function still needs 2 return values, though.
input: remove LIRCCD support

This removes support for the "LIRC Client Daemon", which is separate
from LIRC, and hasn't been maintained for 10 years.

See github issue #413.
Replace mp_tmsg, mp_dbg -> mp_msg, remove mp_gtext(), remove set_osd_tmsg

The tmsg stuff was for the internal gettext() based translation system,
which nobody ever attempted to use and thus was removed. mp_gtext() and
set_osd_tmsg() were also for this.

mp_dbg was once enabled in debug mode only, but since we have log level
for enabling debug messages, it seems utterly useless.