allow downloading audio in more than one language

[sgerwk]

Some streams have more than one audio stream, for example in different languages. As far as I can see, hlsdl can only be instructed to download one.

This could be done by extending the -A option, like -A eng,ger,... etc. The problem is, it seems to me that the resolution/audio selection is hardcoded to be exactly one by the fact that only a single hls_master_playlist structure is used, and that such a structure only indicates a single audio channel. Is that correct? If so, any suggestion about how to change that?