Initial commit of "release.sh" release-building script.

Also the board manager .json file (first attempt)

Remove the "cores" directory from optiboot. These (which were copies of

core files normally distributed with the Arduino IDE or with other boards
(Sanguino, Luminet) have long been so obsolete that they do more harm than
good, and there is now a mechanism for pointing add-on "boards.txt" entries
to the common platform code.

See http://code.google.com/p/optiboot/issues/detail?id=11

Fix duplicate entry