Added support for all variants of Sanguino

I have created a git repository with support for all variants of Sanguino:
* ATmega644
* ATmega644A
* ATmega644P
* ATmega644PA
* ATmega1284
* ATmega1284P

Both 16MHz and 8MHz versions are available.

My repo can be found here: <https://github.com/Lauszus/Sanguino>.

I don't know how your opinion is regarding adding support for other MCU's, but I think these are rather popular and they are also available in a DIP package, so I think it would be nice if they where supported in the official core.