Improve AV-sync; add more API functions; improve documentation

* Add ability to select mixer for SwingMediaPanel
    * Default mixer is used initially
* Add get(Video|Audio)Stream methods
* Remove duplicate documentation in ffmedia classes
* Add API to specify mixer for SwingMediaPanel
* Clean up SourceDataLine on SwingMediaPanel exit

Closes #110 @1h
Closes #107 @15m
Refs #105 @20m
Refs #103 @40m
Merge branch 'master' of https://github.com/IvyBits/JAVI into master

Conflicts:
	src/main/java/tk/ivybits/javi/JPlay.java
	src/main/java/tk/ivybits/javi/media/ffmedia/FFMedia.java
	src/main/java/tk/ivybits/javi/media/ffmedia/FFMediaStream.java
	src/main/java/tk/ivybits/javi/swing/SwingMediaPanel.java
Merge remote-tracking branch 'origin/master'

Conflicts:
	src/main/java/tk/ivybits/javi/swing/SwingMediaPanel.java
Conclude subtitle merge