Added a control set point struct
Added new controller interface, meaningful default min/max values and a p controller that should work (besides one or two mix-ups in directions)
Gave the Yaw a bit more meaning and didn't limit it like roll or pitch
Corrected a sign error
Replaced 3.1415 by the M_PI variable
Actually, meant 2 * M_PI instead of M_PI
Checking for USB errors and signalling whether the copter is in range or not
Minor formatting issues
Fixed a few memory leaks and made the lib able to stay alive when the dongle is disconnected/connected again.

Also, added the ability to check the state of the copter range in the test program.
Added catching of SIGINT when program is running

Also, added extra branch for landing sequence