[boards] stm32f4_discovery board file for some testing
[rotorcraft] v_adapt: limit min/max estimated hover throttle

The adaptive vertical filter estimates the ratio of vertical acceleration over thrust command.
In effect this will now limit the throttle applied in hover between 20% and 75% of max throttle by default.
[rotorcraft] call ahrs_update_gps

This makes AHRS_USE_GPS_HEADING usable on rotorcraft firmware as well.
Thanks Pranay.
[fixedwing] additonals for energy ctrl

better handling for engine out and max_acc can be set in airframe
closes #497
[modules] fix to use amsys airspeed for control
[modules] a little airspeed_amsys cleanup
[mcu_periph] replace gpio_output_[high|low] with gpio_[set|clear]

That means using the already existing gpio_set and gpio_clear from libopencm3 for stm32.
And defining these for the lpc.
set paparazzi_version to v5.1_devel
fix to use ins_alt_dot with baro wen USE_BAROMETER is defined
[modules] angle of attack sensor fix and cleanup
[dox] update comment in state inteface
improve paparazzi_version if git tags are not found
[modules] baro_board: only call event handler if there is new data
[modules] fix warning in baro_board
[modules] baro_amsys: fix for DT to match BARO_READ_PERIODIC_PERIOD
[modules] BARO_x_DT from generated BARO_x_PERIODIC_PERIOD
[modules] baro_amsys: comment to match the other baro sensors
Merge pull request #498 from flixr/gpio_setclear

[mcu_periph] replace gpio_output_[high|low] with gpio_[set|clear]
KroozSD imu driver improvements

Fixed magnetometer axes.
Accel median filter disabled by default.

closes #501
[STM32] Very limited simple SPI1 slave driver

closes #500