#17 S88 Feedback via UDP and Raspberry Pi GPIOs

[Simon Ahrens]

Added two new S88 interfaces:

• udp-s88 receives s88 feedback messages via UDP from a configurable IP/port. Can be used wth s88udp (http://www.s88udp.de), for example.
• pigpio-s88 reads s88 feedback from a Raspberry Pi's GPIOs using the pigpio library.

I've also added these two devices to src/Makefile.am and Configure.ac including checks for required headers and libraries (pigpio).