mkvtoolnix: updated to 42.0.0

Version 42.0.0 "Overtime":

New features and enhancements
* mkvmerge: added an option for creating byte-identical files:
  `--deterministic <seed>`.
* mkvmerge: Matroska reader: mkvmerge will remove the `icpf` atom headers if
  they're present in frames read from Matroska files.
* mkvmerge: MP4 reader: ALAC tracks: the number of channels, sampling
  frequency and bit depth are now taken from the bitstream in order to fix
  bogus values on the container level.
* mkvpropedit: when changing track UIDs the referring elements in existing
  chapters & tags will be updated automatically, too.
* mkvinfo: when the option `-p`/`--hex-positions` is used, element positions
  will be output regardless of the verbosity level.
* mkvinfo: added the option `-P`/`--positions` for showing the position of
  each element in decimal regardless of the verbosity level used.
* mkvinfo: added the option `-o`/`--continue` for continuing processing when
  the first cluster is encountered regardless of the verbosity level
  used.
* mkvinfo: added the option `-a`/`--all` for outputting all sub-elements (even
  cues & seek head entries) and not stopping at the first cluster regardless
  of the verbosity level used.
* MKVToolNix GUI: multiplexer: added an option in the preferences for
  disabling adding cover images from Blu-ray discs.
* MKVToolNix GUI: multiplexer: added mkvmerge's new `--deterministic` option
  in the "additional command-line options" dialog.
* MKVToolNix GUI: header editor:: when changing track UIDs the referring
  elements in existing chapters & tags will be updated automatically,
  too.

Bug fixes
* mkvmerge: HEVC ES parser: fixed a bug in the slice parser calculating the
  size of a field which in turn could have led to the slice's type being read
  wrong.
* mkvmerge: Matroska reader: fixed a segmentation fault when trying to read a
  file that uses header removal compression but no removed bytes are present
  in the track headers.
* mkvmerge: MPEG elementary stream parser: fixed an invalid memory access and
  use of uninitialized memory that could happen under certain
  circumstances.
* mkvmerge: RealMedia reader: fixed a division by zero when all audio
  timestamps were zero.
* mkvmerge: RealMedia reader: fixed an invalid memory access in the video
  frame assembly code triggered by invalid data in the file.

Build system changes
* `std::optional` (C++17 feature) is now used instead of `boost::optional`.
* `std::regex` is now used instead of `boost::regex`.

Other changes
* New man page translations into French, Italian, Russian and Chinese
  Traditional have been added.

(adam)