InfraRed Remote Control

An IR detector/demodulator must be connected to the input RECV_PIN.
This uses the IRremote library:
http://arcfn.com/2009/08/multi-protocol-infrared-remote-library.html

The algorithm: look at the sequence of MARK signals, and see if each one
is shorter (0), the same length (1), or longer (2) than the previous.
Do the same with the SPACE signals.  Hszh the resulting sequence of 0's,
1's, and 2's to a 32-bit value.  This will give a unique value for each
different code (probably), for most code systems.