Flashing a sketch from SD card using 2boot bootloader

This is great.
Martin, I added you as a collaborator to

Eudaldcp, what's your github id?

I spent a lot of time on 2boots, and actually got about 50% done rewriting it using the sdfat library code. It was really hard to debug. I'm hoping that changes when I get the Dragon I ordered (allows breakpoints.)

hold off on putbacks to the repository until I branch (to preserve the current working version.)