Fixed crash of FluidSynth opcodes on Android

This release of the Csound for Android app fixes a bug in the FluidSynth opcodes that caused them to crash. The app includes a new example that shows how to use SoundFonts on Android.

The app also now provides 9 pre-configured sliders and control channels.

Buttons now send both 1 for press and 0 for release, and the trackpad sends x and y while the pointer is moving.

The user guide has been updated with hints on issues and workarounds.