libebml: updated to 1.4.0

Released v1.4.0.

* 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.

* Fixed compilation on Windows wrt. winapifamily.h

* Fixed compilation on Haiku.

* A C++11 compliant compiler is now required. Several of its
features are now used in the source.

* EbmlElement::FindNextElement: fixed a buffer overflow on the
stack by one byte when the first byte read had its upper four bits
unset.

* EbmlCrc32: added a explicit assignment operator with default
implementation as an explicit copy constructor exists (implicit
assignment operators are deprecated in such cases).

* When reading binary elements with a size of 0, the element was
skipped by libebml instead of returned to the calling function.

(adam)