Add support for parsing chapters from MKV files

[tymmesyde]

Hi,
this include changes to support parsing MKV chapters using the recent changes to introduce metadata Chapter interface
This is already implemented for MP4: Nero & QuickTime
Used this doc as reference: https://www.matroska.org/technical/elements.html

Added sample_with_chapters.mkv for mkvSample_withChapters test
Generated with:

;FFMETADATA1
[CHAPTER]
TIMEBASE=1/1000
START=0
END=1999
title=Chapter 1

[CHAPTER]
TIMEBASE=1/1000
START=2000
END=4999
title=Chapter 2

ffmpeg \                                                                                       
  -f lavfi -i testsrc=duration=5:size=320x240:rate=30 \
  -f lavfi -i sine=frequency=440:duration=5 \
  -i chapters.txt \
  -map 0:v -map 1:a -map_chapters 2 \
  -c:v libx264 -c:a aac \
  sample_with_chapters.mkv

[icbaker]

I can't work out how to delete the stale comment made against an old copy of the code, sorry for the duplication.

[srgsf]

I'm not sure how to resolve threads, everything is correct now.