Downloading Live Streams

As an addition to the newly introduced `Downloader`s for HLS, DASH and SS, it would be great if these were also able to download / cache live streams. This would allow to save excerpts from the stream for later playback, kind of like a recording functionality works for DVRs.

Given the flexible nature of the `Cache`, I would assume the main difference to the existing `SegmentDownloader`s would be that the List of Segments wouldn't be static, but would have to be refetched once all `Segment`s from the current `Manifest` are cached.

Are there any plans to add this functionality?