As reported in issue 331, vpxenc encoded incorrect webm file header
on big endian machines. This change fixed that.
Change-Id: I31924ebd476a87f3e88b9b5424540bf781d2b86f
Initial import of the libmkv directory from the webmquicktime[1]
project, at commit fedbda1.
[1]: git://review.webmproject.org/webmquicktime.git
commit fedbda18de899ff94855cb334de7e471036fbf1d
Change-Id: I1564a0ebfa72293fc296ee02178196530dfd90e4