Missed item re increasing max inav accel correction to 3 m/s

Throttle was kept a min if user switched out of ACRO mode while inverted

Limit is applied as trims from accelerometer calibration are copied to
the ahrs object.

Also updated release notes

Also modified some comments in the code re the esc calibration

Scaling of bottom half of throttle was changed from THR_MIN ~ 500.
Previously it was from 0 ~ 500.

Accel throttle's I term is taken from scaled manual throttle

Release Notes updated

A new radio frame could arrive just as the frame time vs current time
check was being executed causing a false positive

Also bug fix to hold yaw on take-off

set_next_WP function was not setting the alt_change_flag properly

This indirectly switches surface tracking on/off which is useful to
avoid tracking the tops of uneven objects when far above the ground

Copter: constrain loiter so that it never commands more than 45 degrees of lean in lat or lon directions

APM_Config.h should be used to overriding the standard parameters but
they still require a definition in config.h or they will be undefined
when built by the mission planner.

Previously we checked if the alt > target_alt but because there is
little to no overshoot with the new accel based alt controller this
check was failing for some users.

An hidden bit of failsafe functionality in the set_mode function was
switching the throttle mode back to THROTTLE_AUTO instead of
THROTTLE_LAND