drawtext: Add fontconfig support

Introduce the `font` option and make it optional to pass a fontfile.

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
Merge commit 'f1b239ec8b38474d31f3bfea1f0b1693774fa432'

* commit 'f1b239ec8b38474d31f3bfea1f0b1693774fa432':
  drawtext: Add fontconfig support

Conflicts:
	configure
	doc/filters.texi
	libavfilter/vf_drawtext.c

See: 40b7a27bad8b8b35cb215bf4f4cba02a00d6f9e2
Merged-by: Michael Niedermayer <michaelni@gmx.at>
x86: move horizontal add macros to x86util

Also port relevant AVX2/XOP optimizations from x264 with permission
to relicense to LGPL from the corresponding authors

Signed-off-by: James Almer <jamrial@gmail.com>
Reviewed-by: "Ronald S. Bultje" <rsbultje@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
x86/dsputil: use HADDD where applicable

Signed-off-by: James Almer <jamrial@gmail.com>
Reviewed-by: "Ronald S. Bultje" <rsbultje@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Support raw dvdsub palette as stored on normal dvd's

This is how the palette is stored on dvd's. Currently
only xbmc passes the palette information to libavcodec
this way.
Check return value of avio_seek and avoid modifying state if it fails

The code still modifies state if the timestamp is not found. Not
sure exactly how to avoid that.
asf hacks
if av_read_packet returns AVERROR_IO, we are done. ffmpeg's codecs might or might not handle returning any completed demuxed packets correctly
added: Ticket #7187, TV Teletext support for DVB EBU Teletext streams
Don't accept mpegts PMT that isn't current
Don't reparse PMT unless it's version has changed
Read PID timestamps as well as PCR timestamps to find location in mpegts stream
Get stream durations using read_timestamp
changed: allow 4 second skew between streams in mov before attempting to seek
fixed: memleak in mpegts demuxer on some malformed (??) mpegts files with too large pes packets

at-visions sample file brokenStream.mpg
Speed up mpegts av_find_stream_info
dxva-h264 Fix dxva playback of streams that don't start with an I-Frame.
add public version of ff_read_frame_flush

We need this since we sometimes seek on the
input stream behind ffmpeg's back. After this
all data need to be flushed completely.