Added features

Changed how to use portclear and portset registers to allow for the
multiple PICxel objects to be declared.  This allows for two or more
independent strands of LEDs to run off of the same board.  There is a
simple demo to show this off.  Also, it should allow for I/O to be used
simultaneously with the LEDs.  I wanted to release this update quickly
so there is some commented-out assembly in the library.