GPIO communication via sysfs.

gpio-sysfs.* is a collection of functions which encapsulate the
reading / writing and interrupt handling to/from GPIO pins
of the raspberry pi.

The demo program gpio-int-test waits for an interrupt for 
3secs on a GPIO pin. If an interrupt has happened it prints out 
"interrupt" otherwise "timeout".

To run it type:

make
sudo ./gpio-int-test 22

which waits then for an interrupt on GPIO pin 22.