Add defines for data and lock safe methods in radioSendData
Standardize exit codes for radioSendData according to stdlib.h
UART driver added with the hope of putting received packets direcly in the command queue, and just accepting outgoing packets one at a time. Doesn't seem to work with transmission currently.
UART driver works with arbitrary callback function for RX
Comment radio auto-calibration code as it's untested, yet recommendeded

This originally used define guards, which caused a warning when compiling
because radioSetStateOff() wasn't getting used anywhere.
Enable radio auto-calibration code for easier testing; off by default
Merge pull request #3 from biomimetics/master

Your changes are now in biomimetics, with some minor cleanup and restructuring