Copter: landing detector checks baro climb rate

Barometer climb rate must be -150cm/s ~ +150cm/s
This threshold is generous because we already use the inertial
navigation climb rate so this is just to catch cases where inertial nav
is very incorrect in it's climbrate estimates
DataFlash: log baro climbrate
Copter: remove debug
Copter: ReleaseNotes for AC3.2-rc13
Frame_params: 3DR_Iris+.param
Add GPS_HDOP_GOOD
AP_InertialSensor: first steps in frontend/backend split

This converts the MPU6000 driver to a frontend/backend structure, and
disables all other drivers. They will be progressively re-enabled as
each is converted
AP_InertialSensor: converted HIL backend, which gets SITL working
SITL: update for new AP_InertialSensor API
AP_InertialSensor: converted PX4 driver to new API
AP_InertialSensor: converted the MPU9250 driver to new API
AP_InertialSensor: converted the APM1/Oilpan driver to new API
AP_InertialSensor: minor tidy up for HIL driver
AP_InertialSensor: improved timing in all drivers
AP_InertialSensor: ported L3G4200D driver to new API
AP_InertialSensor: tidy up MPU6000 driver
AP_InertialSensor: use common AP_InertialSensor driver for PX4 and VRBRAIN
AP_InertialSensor: converted flymaple driver to new API
AP_InertialSensor: converted MPU9150 driver

untested conversion
Plane: update for new AP_InertialSensor API
Copter: convert to new AP_InertialSensor API