Matroska stack update.

libebml 1.4.0:

• Due to breaking ABI the soname version has been bumped to 5.0.0.
• Default symbol visibility is now "hidden", reducing binary size.
• Converted some things pointed out by cppcheck & clang-tidy to C++11.
• Fixed a lot of issues pointed out by clang-tidy.
• Added a function ForceNoDefault in the EbmlElement class.
• Added a function OverwriteData in the EbmlElement class to complement the existing OverwriteHead function.
• A C++11 compliant compiler is now required. Several of its features are now used in the source.

libmatroska 1.6.0:

• libEBML v1.4.0 is now required.
• Due to breaking ABI the soname version has been bumped to 7.0.0.
• Default symbol visibility is now "hidden", reducing binary size.
• Converted some things pointed out by cppcheck & clang-tidy to C++11.
• Fixed a lot of issues pointed out by clang-tidy.
• A C++11 compliant compiler is now required. Several of its features are now used in the source.
• KaxCueData class: added PositionSet overrides taking KaxSimpleBlock arguments.
• KaxSeekHead class: the IndexThis function now returns a pointer to the newly allocated KaxSeek instance.
• KaxBlockData class: the SetReferencedTimecode function is now public.
• Fixed classes for updates in the current specification: KaxTrackTimecodeScale (can be written again), TimeSlice, SliceLaceNumber, TrackAttachmentLink (these cannot be written anymore), KaxContentEncAlgo (it's mandatory), KaxChapLanguageIETF (can occur multiple times), KaxFileUsedStartTime, KaxFileUsedEndTime (DivX-related elements, cannot be written anymore)
• Added classes for new elements from the current specification: KaxBlockAdditionMapping, KaxBlockAddIDValue, KaxBlockAddIDName, KaxBlockAddIDType, KaxBlockAddIDExtraData, KaxContentEncAESSettings, KaxContentEncAESSettings.
• The MATROSKA_VERSION pre-processor definition has been removed. You used to be able toe restrict compiling with only those classes for elements contained in Matroska v1, but that hasn't worked since 2010, so… yeah.