Saves 0.1ms at 100hz

Also removed unused _lean_angle_max variable

This value is for reporting purposes only

Contribution from Leonard Hall

Contributed by Leonard Hall

Contributed by Leonard Hall
This should reduce the aggressiveness of the response when we experience
a GPS glitch

Contributed by Leonard Hall

previously it was 50% ~ 150% of expected mag field but now expanded to
35% ~ 165%.

We now allow the I term even if we've hit the yaw limits as long as
updating the I term will reduce it

Hardly my finest work but it's temporary because we're going to replace
all the led, buzzer etc with a library called AP_Notify in the near
future.

Fence was missing GPS 3D fix check before selecting recovery decision.

SuperSimple bearing was updated without checking for GPS 3D Fix availability.

This helps reduce jumpiness due to althold feed forward

WP_ACCEL added to allow user control of acceleration during missions.
Loiter acceleration made to be half of loiter max speed

Set loiter target and prev iterations velocity when circle mode is
started
Start circling from projected stopping point