Intelligent streaming

[dvdsk]

Currently streaming just downloads the file from the start and starts playback as soon as it has enough data. This has the following problems:

• seeking to the end of a podcast takes almost as long as downloading the podcast this makes resuming a long podcast (after having closed the app) very slow.
• we waste the users data
• we waste the users ram

To fix this:

• make the http stream seekable.
• implement a data structure for keeping already downloaded bits
• keep downloading ahead slightly to prevent stuttering

possible pain points:

• rodio needs the seekable object in its own thread however we do not want to put the download on that thread
• how to communicate downloaded bits