Rewrite file stream with seek function.
1. remove the DZURLSessionForAudioStream.
2. add DZFileStream, taking advantage of fseek, writing stream directly to file.
3. unified file stream for both local and remote file over HTTP.
4. redefine functions of DZCache, limit its function.
5. [TODO] add seek ability to DZAudioQueuePlayer, and complete DZAudioPlayer.