Log Message:
mkvtoolnix: updated to 18.0.0

Version 18.0.0 "Apricity" 2017-11-18

New features and enhancements
* build system: when building with clang v3.8.0 or newer, `configure` will no
  longer restrict optimization flags to `-O1` and use `-O3` again (older
  versions of clang suffered from excessive memory usage with higher
  optimization levels).
* build system: when building with mingw 7.2.0 or newer, `configure` will no
  longer restrict optimization flags to `-O2` and use `-O3` again (older
  versions of mingw suffered from bugs such as segmentation faults with higher
  optimization levels).
* build system: stack protection is enabled when building with clang 3.5.0 or
  newer on all platforms.
* mkvmerge: AVC & HEVC ES parsers: performance improvements by copying much
  less memory around.
* mkvmerge: tags: reintroduced a workaround for non-compliant files with tags
  that do not contain the mandatory `SimpleTag` element. This workaround was
  removed during code refactoring in release v15.0.0.
* GUI: multiplexer: the "AAC is SBR/HE-AAC/AAC+" checkbox in the \ 
"audio
  properties" section will be disabled if the functionality is not implemented
  for the selected track's codec & container.
* GUI: multiplexer: the "reduce to core" checkbox in the "audio \ 
properties"
  section will be disabled if the functionality is not implemented for the
  selected track's codec.

Bug fixes
* mkvmerge: AAC ADTS parser: fixed interpretation of the
  `channel_configuration` header element for ADTS files that do not contain a
  program configuration element: value 7 means 7.1 channels.
* mkvmerge: Matroska identification: the `date_local` and `date_utc`
  attributes will only be output if the identified Matroska file actually
  contains the "date" header field.
* mkvmerge: WebVTT: mkvmerge did not recognize timestamp lines if the hours
  components were absent.
* mkvpropedit, GUI's header editor: the `date` header field won't be added
  automatically anymore whenever the segment info section is edited and the
  `date` element is either deleted or not present in the first place.