add getmediainfo endpoint

[flavioribeiro]

refs to http://api.encoding.com/#APIResponses_GetMediaInfo

{
    "response": {
        "bitrate": "1807k",
        "duration": "6464.83",
        "audio_bitrate": "128k",
        "video_codec": "mpeg4",
        "video_bitrate": "1679k",
        "frame_rate": "23.98",
        "size": "640x352",
        "pixel_aspect_ratio": "1:1",
        "display_aspect_ratio": "20:11",
        "audio_codec": "ac3",
        "audio_sample_rate": "48000",
        "audio_channels": "2"
    }
}

cc @fsouza, @marzagao