Mother forgive me.

Basically bailed on low-power on GPS for the time being, it will go
into low-power tracking though.
Fixed gauge_voltage in gauge implementation.
Added some minor test code to receiver to confirm interrupt operation.
Back receiver code has been (sloppily) implemented, need to fix some
variable names.
LEDGraph has been added, needs some cleaning.
Some shoddy tests have been implemented as real-main variations, I will
be adapting them to the tests folder later.