Improve JavaDoc for StreamPlayerListener.progress

https://github.com/goxr3plus/java-stream-player/blob/4991e4acc52041ca1529404d176c57b4171eba94/src/main/java/com/goxr3plus/streamplayer/stream/StreamPlayerListener.java#L43-L49

Try to answer at least these questions:

- When and how often is progress() called? Who is the caller?
- Clarify nEncodedBytes the n encoded bytes. Does it mean "the number of encoded bytes"? If so, since when? Where are these bytes and where do they come from?
- microsecondPosition the microsecond position: When does the timer start? How often is the value updated? For each call of progress()?
- Is there any guarantee for how it is encoded? If so, how is the pcmData encoded? Apparently it's an array of bytes. How does it encode two or more channels of 16 or more bits per sample?
- What are the properties?