sub: add ASS to RGBA conversion

This makes implementing new VOs easier, because they don't have to
support the ASS format.
vf_scale: support more pixel formats

The RGBA, ARGB, BGRA, ABGR were previously not always supported,
depending on system endianness.
vo/ao: SDL 1.2+ audio driver, SDL 2.0+ accelerated video driver

This mainly serves as a fallback for platforms where nothing better is
available; also as a debugging help. Both the audio and video driver are
not first class - the audio driver lacks delay detection, and the video
driver only supports a single YUV color space.

Configure options: --disable-sdl2 to disable SDL 2.0+ detection,
--disable-sdl to disable SDL 1.2+ detection. Both options need to be
specified to turn off SDL support entirely.
demux_mpg, ass_mp: fix warnings

The warnings in demux_mpg were silenced by additional no-operation
casts.

A variable in ass_mp was used only for some versions of libass; now the
declaration is in that version #ifdef too to avoid a compiler warning.
vdpau: silence a clang warning

It's just some braces...
encoding-example-profiles: fix "oac" typo

Fixes issue #10.
sdl, encode_lavc: fix copyright headers

Some of them had changes in 2012; extend their header.

Fix project name.
vo_opengl: use more precise gamma for BT.709 with color management

Change from gamma 2.2 to the slightly more precise 1/0.45 as per BT.709.

https://www.itu.int/rec/R-REC-BT.709-5-200204-I/en mentions a value of
γ=0.45 for the conceptual non-linear precorrection of video signals.

This is approximately the inverse of 2.22, and not 2.20 as the code had
been using until now.
audio: make de-planarization faster

Uses the same trick as the planarization code to turn per-sample memcpy
calls into mov instructions. Makes decoding a ~25min 48000Hz 2ch floatle
audio file faster from 3.8s to 2.7s.
DOCS: document EDL format

This is taken from the commit message of 968154ba77f8, with some fixes
to make it valid RST.
manpage: minor improvements
core: fix crash if VO init fails
gl_common: properly reject old OpenGL versions

The extension checking logic was broken, which reported OpenGL 3 if the
OpenGL .so exported OpenGL 3-only symbols, even if the reported OpenGL
version is below 3.0. Fix it and simplify the code a bit. Also never
fail hard if required functions are not found. The caller should check
the capability flags instead. Give up on the idea that we should print
a warning if essential functions are not found (makes loading of ancient
legacy-only extensions easier).

This was experienced with the following version strings:

OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) 915GM x86/MMX/SSE2
OpenGL version string: 1.4 Mesa 9.0.1

(Possibly reports a very old version because it has no GLSL support,
and thus isn't even GL 2.0 compliant.)
vo_opengl_old: reject 9-15 bit formats if textures have less than 16 bit

For 9-15 bit material, cutting off the lower bits leads to significant
quality reduction, because these formats leave the most significant bits
unused (e.g. 10 bit padded to 16 bit, transferred as 8 bit -> only
2 bits left). 16 bit formats still can be played like this, as cutting
the lower bits merely reduces quality in this case.

This problem was encountered with the following GPU/driver combination:

OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) 915GM x86/MMX/SSE2
OpenGL version string: 1.4 Mesa 9.0.1

It appears 16 bit support is rather common on GPUs, so testing the
actual texture depth wasn't needed until now. (There are some other Mesa
GPU/driver combinations which support 16 bit only when using RG textures
instead of LUMINANCE_ALPHA. This is due to OpenGL driver bugs.)
vf_scale: prefer 420P10 -> YV12 instead of 444P

Strictly speaking, 444P is higher quality than YV12, but doing this is
not very useful when playing 10 bit video with -vo opengl-old on a GPU
that doesn't support 16 bit textures.
stream_lavf: warn if protocol not found

If ffmpeg returns AVERROR_PROTOCOL_NOT_FOUND, print a warning that
ffmpeg should be compiled with network support. Note that stream_lavf.c
itself includes a whitelist of directly supported ffmpeg protocols, so
it can't happen that a completely unknown/madeup protocol triggers
this message. (Unless the ffmpeg:// or lavf:// prefixes are used.)
vo_sdl: some OSD optimizations

The premultiplied-alpha hack is changed:

- The first stage now uses a colormod of black with an unmodified
  texture. This saves on applying the AND mask of 0xFF000000 to keep
  alpha only.

- The second stage no longer uses an AND mask, but only an OR mask of
  0xFF000000 to cancel out alpha.

- The texture uploads are no longer done using SDL_LockTexture,
  SDL_ConvertPixels, SDL_UnlockTexture when the mpv pixel format matches
  the OSD's pixel format. Instead, SDL_UploadTexture is used, which
  saves a copy when using the "opengl" renderer.
vo_sdl: support -geometry properly

Now the x and y origin options (-geometry WxH+X+Y) are supported too.
cocoa_common: add support for `--no-border`

Draw a window with style NSBorderlessWindow when the user uses `--no-border`.
Update copyright year