Bump library version to 2.4.0

Fix LowLevelEngine example

Remove amplitude check restrictions on AudioSample (closes #93)

Don't probe output devices on Android

Prevent ArrayIndexOutOfBoundsException when none of the devices have …

…any inputs

Implement mp3/ogg/.. SoundFile decoding using JavaSound

This will break Android support to some extent, but fixes #32 by
switching to the much more well-supported (and 4x faster!) mp3spi,
closes #53 by adding support via vorbisspi, and also fixes #15 since 8
bit wav files are are now simply decoded through JavaSound.

Load PortAudio when LineUnsupportedException occurs (refs #85)

Update Javadoc

Add constructor argument and method to SoundFile to control caching (…

…implements #47)