Copter: remove command_description.txt

Description in this file were out of date or incomplete and it is better
for people to refer to the MAVLink documentation or the
/libraries/GCS_MAVLink/message_definitions/common.xml and
ardupilotmega.xml files
AutoTest: add AVC_copter to location

The existing AVC location is for Rovers.  Planes and copters take-off
from a position slighly further north.
Copter: enable PARACHUTE and RALLY for all but APM
Copter: AC3.2-rc2 release notes and version
Copter: remove unused pos vector functions

removed pv_latlon_to_vector, pv_get_lat, pv_get_lon.
it would probably be best if these were moved into the Math library
GCS_MAVLink: moved 3 more send_*() functions to GCS_Common.cpp
Rover: use new GCS_Common.cpp functions
Copter: use new GCS_Common.cpp functions
Plane: use new GCS_Common.cpp functions
AntennaTracker: use new GCS_Common.cpp functions
Copter: release notes for AC3.1.5
AC_PID: Add new AC_HELI_PID as a child of AC_PID
AC_PID: Change Private members to Protected so that AC_HELI_PID can access them.
AC_PID: update example sketch to test AC_HELI_PID
Copter: Change TradHeli to use new AC_HELI_PID class.
AC_AttitudeControl_Heli: Change to use AC_HELI_PID class instead of AC_PID.  Remove FF parameters from class.
AC_PID: Remove get_leaky_i function which is now found in AC_HELI_PID.
AC_PID: Add method to set the D-term Filter Rate from main code.
Copter: Set Rate PID D-term filter rates on initialization.
Copter: Add 'handle' to allow #define updating of AC_PID filter rate for Throttle Accel.