Convert mkv files to mp4

Current version

Revision: 1

mkvtomp4 requires the following formulae to be installed:
gpac 0.7.1 Multimedia framework for research and academic purposes
ffmpeg 3.4 Play, record, convert, and stream audio and video
mkvtoolnix 18.0.0 Matroska media files manipulation tools

Formula history

Mike McQuaid Use hash rockets again. (#5177)
Mike McQuaid Use Ruby 1.9+ symbol hash keys in all formulae. (#4942)
Zhiming Wang mkvtomp4: revision for ffmpeg update
Nikolaus Wittenstein Add descriptions to all remaining homebrew packages
Mike McQuaid mkvtomp4: don't depend on :python.
Mike McQuaid mkvtomp4: fix PYTHONPATH handling.
Mike McQuaid mkvtomp4 1.3
Mike McQuaid mkvtomp4: cleanup python usage.
Alex K mkvtomp4 1.2