Fixed sample for duration and added sample for codec_name
Fixed sample for duration and added sample for codec_name

I've updated the README file, because the existing example for getting the duration of a file was not working for file-types like WebM (see #103).

To not to loose the sample that was already in place, I changed it to return the codec-name for the video. Maybe returning width or height of a video is more used, but we can't have a sample for all ;)

soluciones-gbh/PHP-FFMpeg,curtisdf/PHP-FFMpeg,alawnchen/PHP-FFMpeg,gcc-roblox/gcc-roblox.github.io,we-bridge/PHP-FFMpeg,beeseenmedia/PHP-FFMpeg,lb0913/PHP-FFMpeg,superdol/PHP-FFMpeg,burzum/PHP-FFMpeg,mruse/PHP-FFMpeg,Pixy/PHP-FFMpeg,NAMEs/PHP-FFMpeg,gcc-roblox/gcc-roblox.github.io,alawnchen/PHP-FFMpeg