#35 Add feature to call ffmpeg directly.

[rdwvk]

I'm on hosting where shell_exec disabled due to security reasons.
Good news: ffmpeg-php extension is installed.
Bad news: it gives me an error and google doesn't help.
Good news: executing "ffmpeg bla-bla-bla" on ssh results in what I need.
Bad news: there is no way to execute ffmpeg shell command using ffmpeg-php directly.

I'm asking you to implement this feature with separate function like "ffmpeg_raw($args)". Probably that's not so difficult but will help people that are facing security issues i've ran into.