player: update playback position on seek

If the actual PTS is not known yet right after a seek, the "time-pos"
property will just return the seek target PTS. For this purpose, trigger
a change event to make the client API update the "time-pos" and related
properties. (MPV_EVENT_TICK triggers this update.)
vdpau: don't upload video images in advance

With software decoding, images were uploaded to vdpau surfaces as they
were queued to the VO. This makes it slightly more complicated
(especially later on), and has no advantages - so stop doing it.

The only reason why this was done explicitly was due to attempts to keep
the code equivalent (instead of risking performance regressions). The
original code did this naturally for certain reasons, but now that we
can measure that it has no advantages and just requires extra code, we
can just drop it.
manpage: lua: document timer timeout and oneshot fields

Might be useful for scripts, so document them. (Which means scripts
are allowed to use them, without risking breakage.)
player: allow precise seeking with percent seeks

I'm not sure why this was explicitly disabled. It's from mplayer2 times.