Only use GPIORs if they are actually available for the target MCU
Added support for atmega64 (yes, this is a bit of a hack).
define for Teensy 3.1
Merge pull request #17 from PaulStoffregen/master

define for Teensy 3.1
Use second serial on atmega64
Merge pull request #18 from raumzeitlabor/pull-1

Only use GPIORs if they are actually available for the target MCU