Added SandStorm Avionics Software/GPS_balloon/GPS_balloon.ino (in a directory
to facilitate easier sketchbook management).

This file lack the SD card functionality, but adds control for the still
camera using digital pin 8.  New variables:

* static const int CamPin = 8
* unsigned int photo_interval = 30; // seconds
* unsigned int photo_duration = 1000; // milliseconds
* bool photo_state = false;

The Arduino will activate the camera every [photo_interval] seconds, after
which the [CamPin] will remain HIGH for [photo_duration] milliseconds.

For debugging purposes, the built-in LED on pin 13 is currently lit when
[photo_state] is true.

Changed altitude and speed fields in the CSV output to use meters and kmph,
respectively, mostly due to the values Google Earth expects by default.