[dev-context] three rendition options

Hi Hans, Michal Vlasák send me the attached patch to be able to set volume, opacity and repeat for renditions, such as in: \setupinteraction[state=start] \starttext \null\page \definerenderingwindow[myrenderingwindow] [width=\textwidth, height=\textwidth, openpageaction=StartRendering{\currentrendering}, closepageaction=StopRendering{\currentrendering}] \startTEXpage[offset=1ex, pagestate=start] \userendering[key-name][video/mp4][video.mp4] [embed=yes, volume=25] \placerenderingwindow[myrenderingwindow][key-name] \stopTEXpage \null\page \stoptext He asked me to submit the patch to ConTeXt to be merged, since he lacks the free time to submit it himself. Many thanks for your help, Pablo