Specify output filename

Adds the ability to specify an output file name to the script.

When transcoding a TV series (from DVD) it is necessary to be able to specify the output format. For example the disc for The X-Files Season 1 Eps 1-4 is named "XFILES_DISC1" and when you want to transcode all episodes you have to manually rename the generated files. Being able to specify the output name solves this.

I have made the option such that it remains the current functionality, but allows to override the default name generation.