these changes were intended for the previous commit

These paragraphs, taken from the previous commit log, go with the
changes that are committed now.

RPiGPIO.class.php: Commented code a bit. Removed default GPIO pin number
and added some code to loosely enforce for valid GPIO pin numbers. This
appears to work well now, though unit testing would be good.

rfid_key.class.php: Added author and related comments.  Removed all
comments and code that were not specific to basic RFID-key parsing and
handling. In other words, all non-rfid stuff that might be related to a
given rfid-key, was removed to make this concept clean and simple.
People now have a RFIDs rather than the other way around.