Fix for looping after an audio decode error is encountered
Issue #20 - Added extra joystick inputs and other input improvements.

- support all joystick axes and buttons supported by SFML (8 joysticks w/
8 axes and 32 buttons per stick)
- improved handling of analog joysticks
- added 'joystick threshold' and 'mouse threshold' user config settings
- added fe.get_input_state() and fe.get_input_pos() layout/plugin script
commands