Adding board definitions for #89

[Doom4535]

Highlights

Added entries for additional boards in #89:

• Nano (technically v3, v2.x looks to have used the atmega168)
• Mega1280
• Adafruit Grand Central M4 Express

Issues Fixed

Changed processor used for Arduino due from atmega/avr to atmel sam

Notes

• No action has been taken as of yet to expose additional analog pins on Nano
• No action has been take to expose additional features of the Grand Central beyond the standard M4 at this time

[Doom4535]

Welp, this is what I get for thinking these changes could be made from mobile only.

[ianfixes]

This looks like a good start. Don't be too concerned about the compiler errors, this simply means that we need to do some intelligent mocking out of defines, possibly in cpp/arduino/ArduinoDefines.h.

The most ominous warning (about device type not defined) is coming direction from avr/io.h, where I don't see __AVR_ATSAM3X8E__ listed.

Could it be that I'm using an outdated set of library files from the Arduino library (io.h in particular)?

[ianfixes]

Reposting on #124 which seems to be a duplicate/repeat of this issue.