This update brings the mkvtoolnix/libmatroska/libebml stack to the latest upstream release. See respective changelogs for list of changes:

mkvtoolnix: https://www.bunkus.org/videotools/mkvtoolnix/doc/ChangeLog

libmatroska: * build system: switched the build system from hand-crafted Makefiles to an autoconf/automake-based system. A pkg-config file will be installed as well; its name is »libmatroska«. Based on a similar patch for libEBML by Jan Engelhardt jengelh@inai.de. * KaxBlock::ReadData(): fixed several instances of unchecked memory access leading to invalid memory access/segmentation faults with invalid or broken data inside block groups/simple blocks. * KaxBlock::ReadInternalHead(): fixed a off-by-one buffer overflow if with EBML lacing and exactly one frame in the lace.

libebml: * EbmlElement::Render(): doesn't catch exceptions anymore. Instead exceptions generated from the IOCallback class (e.g. if a write failed) are propagated to the caller. * build system: switched the build system from hand-crafted Makefiles to an autoconf/automake-based system. A pkg-config file will be installed as well; its name is »libebml«. Patch by Jan Engelhardt jengelh@inai.de. * EbmlMaster::Read(): when reading with SCOPE_ALL_DATA only those elements that could successfully be read will be kept (e.g. defective block groups will be dropped). * EbmlMemoryStream: add a new class for safe memory access that throws exception on failures. * EbmlMaster: Fixed read() trying to calculate the end position of elements with an unknown size. This avoids endless loops and assertions in certain cases. See https://trac.bunkus.org/ticket/1089