libmatroska: updated to 1.7.0

Version 1.7.0 2022-09-30

* A C++14 compliant C++ compiler is now required.
* libEBML v1.4.3 is now required.
* Remove Coremake project files
* Add `KaxInternalBlock::GetRelativeTimestamp()` to access unscaled
  block timestamps.
* Fixed problems with the generated `pkg-config` files if any of the
  installation paths are absolute.
* Added several enums in `namespace libmatroska` for the various
  elements that are constrained to a set of options:
  `MatroskaTrackType`, `MatroskaTrackEncodingCompAlgo`,
  `MatroskaChapterTranslateCodec`, `MatroskaTrackTranslateCodec`,
  `MatroskaVideoFlagInterlaced`, `MatroskaVideoFieldOrder`,
  `MatroskaVideoStereoMode`, `MatroskaVideoAlphaMode`,
  `MatroskaVideoOldStereoMode`, `MatroskaVideoDisplayUnit`,
  `MatroskaVideoAspectRatioType`, `MatroskaVideoMatrixCoefficients`,
  `MatroskaColourChromaSitingHorz`, `MatroskaColourChromaSitingVert`,
  `MatroskaVideoRange`, `MatroskaVideoTransferCharacteristics`,
  `MatroskaVideoPrimaries`, `MatroskaVideoProjectionType`,
  `MatroskaAudioEmphasis`, `MatroskaTrackPlaneType`,
  `MatroskaContentEncodingScope`, `MatroskaContentEncodingType`,
  `MatroskaContentEncodingAlgo`, `MatroskaAESSettingsCipherMode`,
  `MatroskaContentSignatureAlgo`, `MatroskaContentSigHashAlgo`,
  `MatroskaChapterSkipType`, `MatroskaChapterProcessTime` and
  `MatroskaTargetTypeValue`.
* Updated the semantics to the latest specifications, deprecating the
  following elements by preventing code to write them:
  `KaxClusterSilentTracks`, `KaxClusterSilentTrackNumber`,
  `KaxSlices`, `KaxReferenceFrame`, `KaxReferenceOffset`,
  `KaxReferenceTimeCode`, `KaxTrackTimecodeScale`,
  `KaxCodecDecodeAll`, `KaxVideoAspectRatio`, `KaxTrickTrackUID`,
  `KaxTrickTrackSegmentUID`, `KaxTrickTrackFlag`,
  `KaxTrickMasterTrackUID`, `KaxTrickMasterTrackSegmentUID`,
  `KaxContentSignature`, `KaxContentSigKeyID`, `KaxContentSigAlgo` and
  `KaxContentSigHashAlgo`.
* Updated the semantics to the latest specifications, making the
  following elements mandatory (but having default values):
  `KaxCodecDelay`, `KaxVideoPixelCropBottom`, `KaxVideoPixelCropTop`,
  `KaxVideoPixelCropLeft`, `KaxVideoPixelCropRight`,
  `KaxVideoBitsPerChannel`, `KaxCueCodecState`,
  `KaxTagTargetTypeValue`, `KaxTrackLanguage`, `KaxVideoStereoMode`,
  `KaxVideoAlphaMode`, `KaxEditionFlagOrdered`,
  `KaxVideoChromaSitHorz`, `KaxVideoChromaSitVert`,
  `KaxVideoColourRange`, `KaxVideoColourMatrix`,
  `KaxVideoColourTransferCharacter`, `KaxVideoColourPrimaries` and
  `KaxVideoDisplayUnit`.
* Updated the semantics to the latest specifications, removing the
  default values from the following elements: `KaxCueBlockNumber`,
  `KaxFlagHearingImpaired`, `KaxFlagVisualImpaired`,
  `KaxFlagTextDescriptions`, and `KaxFlagOriginal`.
* Updated the semantics to the latest specifications, adding the
  following new elements: `TagDefaultBogus` (as a placeholder for
  accidentally used but wrong EBML ID 0x44b4), `KaxEmphasis`,
  `KaxChapterSkipType`, `KaxEditionDisplay`, `KaxEditionString` and
  `KaxEditionLanguageIETF`.

(adam)