vf_rotate: fix params >= 4
mp_image: copy palette only if allocated

Normally, we assume that IMGFMT_PAL8 always has a palette allocated
in plane 1. But there may be corner cases in ffmpeg where it doesn't
(namely pseudo-pal stuff).
video: add a new method to configure filters and VOs

The filter chain and the video ouputs have config() functions. They are
strictly limited to transfering the video size and format. Other
parameters (like color levels) have to be transferred separately.

Improve upon this by introducing a separate set of reconfig() functions,
which use mp_image_params to carry format parameters. This struct
contains all image format related parameters from config(), plus
additional parameters such as colorspace.

Change vf_rotate to use it, as well as vo_opengl. vf_rotate is just
an example/test case, but vo_opengl will need it later.

The intention is also to get rid of VOCTRL_SET_YUV_COLORSPACE. This
information is now handed to the VOs via reconfig(). The getter,
VOCTRL_GET_YUV_COLORSPACE, will still be needed though.
vo_opengl: handle chroma location

Use the video decoder chroma location flags and render chroma locations
other than centered. Until now, we've always used the intuitive and
obvious centered chroma location, but H.264 uses something else.

FFmpeg provides a small overview in libavcodec/avcodec.h:

-----------
/**
 *  X   X      3 4 X      X are luma samples,
 *             1 2        1-6 are possible chroma positions
 *  X   X      5 6 X      0 is undefined/unknown position
 */
enum AVChromaLocation{
    AVCHROMA_LOC_UNSPECIFIED = 0,
    AVCHROMA_LOC_LEFT        = 1, ///< mpeg2/4, h264 default
    AVCHROMA_LOC_CENTER      = 2, ///< mpeg1, jpeg, h263
    AVCHROMA_LOC_TOPLEFT     = 3, ///< DV
    AVCHROMA_LOC_TOP         = 4,
    AVCHROMA_LOC_BOTTOMLEFT  = 5,
    AVCHROMA_LOC_BOTTOM      = 6,
    AVCHROMA_LOC_NB             , ///< Not part of ABI
};
-----------

The visual difference is literally minimal, but since videophiles
apparently consider this detail as quality mark of a video renderer,
support it anyway. We don't bother with chroma locations other than
centered and left, though.

Not sure about correctness, but it's probably ok.
csputils.h: don't recursively include libavcodec header

Some functions (avcol_spc_to_mp_csp() etc.) used libavcodec enum types
as parameters. Remove these in order to get rid of the avcodec.h
include statement. This prevents that avcodec.h is recursively
included by dozens of files. Fix mp_image.c, which used the header
without explicitly including avcodec.h.
cocoa_common: uninit fs window properly

In fullscreen `s->window` is the windowed window. So freeing that didn't get
rid of the FS window and OpenGL view.

Fixes #122
[ci skip]
command: add properties for playlist position

playlist-pos can set/get the current playlist index. playlist-count
returns the number of entries in the playlist.
command: make raw percent-pos property return fractions

percent-pos was an integer (0-100). Sometimes higher precision is
wanted, but the property is this way because fractional parts would
look silly with normal OSD usage. As a compromise, make percent-pos
double (i.e. includes fractional parts), but print it as integer.

So ${percent-pos} is like an integer, but not ${=percent-pos}.
input: handle mouse movement differently

Before this commit, mouse movement events emitted a special command
("set_mouse_pos"), which was specially handled in command.c. This was
once special-cased to the dvdnav and menu code, and did nothing after
libmenu and dvdnav were removed.

Change it so that mouse movement triggers a pseudo-key ("MOUSE_MOVE"),
which then can be bound to an arbitrary command. The mouse position is
now managed in input.c. A command which actually needs the mouse
position can use either mp_input_get_mouse_pos() or mp_get_osd_mouse_pos()
to query it. The former returns raw window-space coordinates, while the
latter returns coordinates transformed to OSD- space. (Both are the same
for most VOs, except vo_xv and vo_x11, which can't render OSD in
window-space. These require extra code for mapping mouse position.)

As of this commit, there is still nothing that uses mouse movement, so
MOUSE_MOVE is mapped to "ignore" to silence warnings when moving the
mouse (much like MOUSE_BTN0).

Extend the concept of input sections. Allow multiple sections to be
active at once, and organize them as stack. Bindings from the top of
the stack are preferred to lower ones.

Each section has a mouse input section associated, inside which mouse
events are associated with the bindings. If the mouse pointer is
outside of a section's mouse area, mouse events will be dispatched to
an input section lower on the stack of active sections. This is intended
for scripting, which is to be added later. Two scripts could occupy
different areas of the screen without conflicting with each other. (If
it turns out that this mechanism is useless, we'll just remove it
again.)
manpage: document input sections
command: add commands to enable/disable input sections

For now, it's mostly for testing. It also might allow to create key
binding state machines, but this sounds questionable.
input: trigger mouse_leave key bindings if mouse leaves mouse area

Also, implement mouse leave events for X11. But evne on other
platforms, these events will be generated if mouse crosses a section's
mouse area boundaries within the mpv window.
mplayer: don't hide mouse cursor if mouse is inside mouse area
w32_common: refactor mouse button code, handle mouse up events

Instead of sending a single event on click, send both down and up
events.
w32_common: prevent that window dragging and mouse input interfere
input: don't keep separate sections for builtin key bindings

Instead mark individual key bindings as builtin.

Not sure whether this is conceptually simpler or more complicated.
For one, it requires the annoying remove_binds() function to wipe
existing bindings instead of just killing the section, on the other
hand it gets rid of almost all special handling of builtin vs. normal
sections.
input: store number of keys, instead of using 0-termination
input: store number of binds, instead of using 0-termination
sub: update subtitle time offset even if paused

This was changed as part of commit b44202b as an intended
simplification, but it's actually nicer to have the subtitles
update immediately even if paused.
command: redraw subs if sub-delay is changed

Though in practice this probably happened anyway, because OSD was
redrawn.