CLI qscale parameter is not available

[tobystaines]

fnExtractFrameToJPG seems to save images at a lower quality than the original video. With the ffmpeg CLI you can use the -qscale:v parameter to define the output image quality but this doesn't seem to be available in node-ffmpeg. Could it be added?

There is already an open pr which would seem to address this (although I haven't reviewed the code): #53