ffv1: update to ffv1 version 3

Based on code from Carl Eugen Hoyos, Michael Niedermayer and Paul B Mahol.
ARM: reinstate optimised intmath.h

Use of the ARM optimised intmath.h was accidentally dropped in 9734b8b.

Signed-off-by: Mans Rullgard <mans@mansr.com>
doc/platform: Move a caveat down to the notes section

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
doc/platform: Add info on shared builds with MSVC

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
ffv1: Add missing #includes to header file
fate: Introduce ENCMUX macro for tests that require encoders and a muxer
svq3: K&R formatting cosmetics
Merge commit '2d09b36c0379fcda8f984bc8ad8816c8326fd7bd'

* commit '2d09b36c0379fcda8f984bc8ad8816c8326fd7bd':
  doc/platform: Add info on shared builds with MSVC
  doc/platform: Move a caveat down to the notes section
  ARM: reinstate optimised intmath.h
  ffv1: update to ffv1 version 3

Conflicts:
	doc/platform.texi
	libavcodec/ffv1.c
	libavcodec/ffv1.h
	libavcodec/ffv1dec.c
	libavcodec/ffv1enc.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'a7d2861d36756b913e85681b86ed3385274e8ced'

* commit 'a7d2861d36756b913e85681b86ed3385274e8ced':
  svq3: K&R formatting cosmetics
  fate: Introduce ENCMUX macro for tests that require encoders and a muxer
  ffv1: Add missing #includes to header file

Conflicts:
	libavcodec/ffv1.h
	libavcodec/svq3.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
lavc: add lavfi metadata support.

This commit introduces a new AVPacket side data type:
AV_PKT_DATA_STRINGS_METADATA. Its main goal is to provide a way to
transmit the metadata from the AVFilterBufferRef up to the AVFrame. This
is at the moment "only" useful for lavfi input from libavdevice:
lavd/lavfi only outputs packets, and the metadata from the buffer ref
kept in its context needs to be transmitted from the packet to the frame
by the decoders. The buffer ref can be destroyed at any time (along with
the metadata), and a duplication of the AVPacket needs to duplicate the
metadata as well, so the choice of using the side data to store them was
selected.

Making sure lavd/lavfi raises the metadata is useful to allow tools like
ffprobe to access the filters metadata (it is at the moment the only
way); ffprobe will now automatically show the AVFrame metadata in any
customizal output format for users. API users will also be able to
access the AVFrame->metadata pointer the same way ffprobe does
(av_frame_get_metadata).

All the changes are done in this single commit to avoid some memory
leaks: for instances, the changes in lavfi/avcodec.c are meant to
duplicate the metadata from the buffer ref into the AVFrame. Unless we
have an internal way of freeing the AVFrame->metadata automatically, it
will leak in most of the user apps. To fix this problem, we introduce
AVCodecContext->metadata and link avctx->metadata to the current
frame->metadata and free it at each decode frame call (and in the codec
closing callback for the last one).  But doing this also means to update
the way the tiff decoder already handles the AVFrame->metadata (it's the
only one decoder handling metadata at the moment), by making sure it is
not trying to free a pointer already freed by the lavc internals.

The lavfi/avcodec.c buffer ref code is based on an old Thomas Kühnel
work, the rest of the code belongs to the commit author.

Signed-off-by: Thomas Kühnel <kuehnelth@googlemail.com>
Signed-off-by: Clément Bœsch <ubitux@gmail.com>
lavfi/select: store scene score in buf ref metadata.
lavfi/silencedetect: export silence info to metadata.