input: ignore modifiers on MOUSE_LEAVE

Just in case something adds shift/alt/ctrl state to it.
input: remove minor code duplication
input: discard key history when a key is mapped

This is for the sake of multi-key combinations (see github issue #718).
Now a multi-key sequence isn't matched if any of the previous keys were
actually mapped.
input: make key binds order-independent again

This is for the sake of multi-key commands again. This could break:

   SPACE ignore
   SPACE-SPACE command

while this worked:

   SPACE-SPACE command
   SPACE ignore

The reason being that if the shorter command was first in the list,
it would obviously match, and searching was stopped.
lua: add example to rebuild the status line

This can be used to easily extent the status line for one's own needs.

I'm not experienced with lua so a few things could probably be done a
better way.
encode: disable keep-open when encoding
manpage: add notes when to use/not use certain AO and VO drivers
vf_eq: remove slow inline asm

Compiled with -O2, the C code runs just as far (or even slightly faster)
then the MMX inline asm.
vf_ilpack: remove inline asm

This makes it multiple times slower. However, the output format (packed
YUV) isn't handled efficiently by anything to begin with, and I have no
clue we even have this filter. I guess it's one of these filters which
find some use sometimes, but are not of higher importance, which
justifies removing the faster inline asm.
vf_noise: remove line asm

I didn't test the speed, but by default, this filter diverts to
libavfilter already. So this would help only if libavfilter is disabled,
or libavfilter doesn't have vf_noise (like on Libav). For these cases,
we still provide the (possibly but not necessarily) slower C
implementation of vf_noise.
vf_pullup: remove inline asm

No change in speed (or even slightly faster, though I tested with
progressive solid color video only), and normally we use libavformat's
vf_pullup anyway.
vf_divtc: remove inline asm

Becomes a bit slower (tested with progressive solid color video only),
but this filter is pretty obscure and I'm not even sure what it's useful
for.
vf_pp: use native libpostproc CPU detection
vf_pp: fix include statement
Remove CPU detection and inline asm handling

Not needed anymore. I'm not opposed to having asm, but inline asm is too
much of a pain, and it was planned long ago to eventually get rid fo all
inline asm uses.

For the note, the inline asm use that was removed with the previous
commits was almost worthless. It was confined to video filters, and most
video filtering is now done with libavfilter. Some mpv filters (like
vf_pullup) actually redirect to libavfilter if possible.

If asm is added in the future, it should happen in the form of external
files.
Fix some libav* include statements

Fix all include statements of the form:

   #include "libav.../..."

These come from MPlayer times, when FFmpeg was somehow part of the
MPlayer build tree, and this form was needed to prefer the local files
over system FFmpeg.

In some cases, the include statement wasn't needed or could be replaced
with mpv defined symbols.
encode: don't apply default config options

Often, user configs set options that are not suitable for encoding.
Usually, playback and encoding are pretty different things, so it makes
sense to keep them strictly separate. There are several possible
solutions. The approach taken by this commit is to basically ignore the
default config settings, and switch to an [encoding] config profile
section instead. This also makes it impossible to have --o in a config
file, because --o enables encode mode.

See github issue #727 for discussion.
encode: don't resume playback when encoding

The previous commit doesn't handle additionally loaded config files,
such as the playback resume mechanism.