[mcu] Added i2c3 initializationto mcu.c

closes #489
[ardrone2_raw] Battery readout for ARDrone2 RAW version. Formula to convert from 10bit ADC value to battery voltage can be improved
[boards] ardone2: correct voltage scale, thx Eric
[peripherals] updates to l3g4200 gyro from Eduardo
[imu] new GL1 driver from Eduardo

IMU from Goodluckbuy with L3G4200, ADXL345 and HMC5883.
[dox] fix filename in doxygen header
[rotorcraft] only reset psi and integrators if previous mode was not attitude
[imu] aspirin_2_spi: default AHRS_PROPAGATE_FREQUENCY is 512

With DLPF_256HZ (value zero) the internal sampling rate is 8kHz and with a sample rate divider of 1
the output freq was actually 4kHz and not 500Hz. Since the data is polled from the mpu at PERIODIC_FREQUENCY
the AHRS_PROPAGATE_FREQUENCY (defaulting to PERIODIC_FREQUENCY) is also 512Hz for a default rotorcraft config.

Set the output freq to 2kHz now, AHRS_PROPAGATE_FREQUENCY stays at PERIODIC_FREQUENCY=512Hz so doesn't have to be
defined in the airframe file.

Also added defaults for PERIODIC_FREQUENCY of 60 and 120Hz:
- DLPF_42HZ
- output rate of 100Hz
In these cases add <define name="AHRS_PROPAGATE_FREQUENCY" value="100"/>
20s timeout and max 2 retries when trying to update_google_version
[lpc21][uart] fix some unused arg warnings
[modules] silence some warnings in imu_chimu
[fix][lpc21] workaround for init of spi_slave_hs
[boards] correct include guard for apogee 1.0
[conf] configurable spi for aspirin_2
[lisa] comments for the tunnel
[rotorcraft] ins_int_extended without sonar
[rotorcraft] AHRS_FLOAT flag for float_cmpl_quat
[rotorcraft][stabilization] move some macros
[rotorcraft] CAUTION! stabilization int_quat ref model scaling fixes

Now the attitude reference should finally have the correct scaling.

For end users that means it is not so sluggish on RC input anymore and you should get a snappy reference.
CAUTION! Test fly carefully, you might need to lower the gains.
[rotorcraft][stabilization_ref_quat] saturate rate and trim accel