Initial (untested) effort to port to Teensy 3.1

Here's a first attempt to port to Teensy 3.1.  This code is untested, but I'm pretty sure it doesn't alter anything when compiling for Arduino Mega.

Here's the conversation that led to this effort.

http://forum.pjrc.com/threads/26002-OnStep-telescope-control-on-teensy

I hope this pull request helps.  :)