This change lays the groundwork for adding support for Rev 3 3B2 models,
which includes the Model 500, Model 600, and Model 1000.
Rather than use the fixed strings "400" and "1000" in file names, the
strings "rev2" and "rev3" will be used, which allows greater flexibility
to implement various system configurations more easily.
Additionally, this change adds a copy of the Debug Monitor (DEMON) ROM
image for the Rev 2 board, to be used soon in a later checkin.
Refactor in preparation for the addition of a Rev 3 simulator for the
3B2/1000 system.
This change also includes a full cleanup of the rat's-nest of includes
and externs that plagued the 3B2 simulator and made it difficult to
understand and maintain. Headers are now required in the following
order:
compilation unit -> "3b2_defs.h" -> {... dependencies ...}
Finally, HELP has been added to the CPU device.
