Move the tone_alarm driver out of the NuttX configs area and add it as an stm32-specific driver in the PX4 apps space.

Add a new tone_alarm command that can be used to start/stop alarm tones from the shell.

Add functions for computation of the distance and bearing to the nearest point of a line segment or arc segment.

Fix stack allocation (now probably too large) for PX4IO debugging.  Disable nonblocking serial comms to avoid losing tx data.

Make it possible to run fmu and px4io simultaneously with full control over both sets of possible PWM outputs.  First started wins.