This is a collection of modules to provide a hardware abstraction
layer for the AVR architecture.

delay.h    --- provides timing delay routines.
eeprom.h   --- provides routines for reading/writing EEPROM memory for non-volatile storage.
pacer.h    --- provides routines for constructing paced loops using timer 1.
pio.h      --- provides routines for accessing the I/O ports.  Note pio.h uses
           advanced techniques; I suggest looking at pio-simple.h and pio-simple.c for a much simpler implementation.
system.h   --- system dependent definitions, such as CPU speed and pin allocations.
config.h   --- common configuration definitions.