Copter: re-order init_sonar

No functional change.
ArduPilot: update README.md
ArduPilot: fixup README format
AP_InertialSensor: fixed default MPU9250 orientation for NavIO
AP_TECS : Prevent throttle undershoot after climb

If the plane was unable to achieve the climb and got significantly below the internal TECS demanded climb profile, the the PD term would be a large value at the top of climb, and would take some time to reduce due to the rate limiter. This meant that the integrator state could be pushed to a very low value and effectively cause the throttle to sit on the lower limit for longer than desired after levelling out.
AP_TECS: fixed throttle demand on underspeed

thanks to Philipp Oettershagen for finding this bug!