Plane: fixed stick mixing in AUTO modes

the mixing was asymmetric. Many thanks to Soren Kuula for noticing this!
autotest: added generation of Parameters.html for wordpress

this generates APM docs for wordpress
Copter: WPNav consolidate acceleration #defines
Copter: don't spin motors in ALTHOLD with zero throttle
Copter: scaling stability patch
Copter: enable GPS failsafe by default
autotest: update rover sim for turning circle based steering

more realistic modelling of a rover
autotest: make rover sim closer to Toms slash
Rover: fixed change of speed command

m/s not cm/s
SITL: added SIM_MAG_ERROR parameter

this is a compass yaw error in degrees, used for testing navigation
with a bad compass
Copter: beep twice during arming
autotest: fixed initial yaw in copter sim
scripts: added auto upload of parameters to new wordpress wiki
scripts: fixed plane auth for wordpress upload
autotest: fixed escaping of html in wiki descriptions
Plane: improve ALT_MIX docs
autotest: added advanced param warning and header to auto-docs
autotest: stop updating google code parms, and add separate vehicle parms

We have moved the google code parms to wordpress

this allows GCS developers to pull only the parameters for the vehicle
they are flying if they prefer.
Plane: removed the old crash_timer code

This code is less relevent with the new L1 navigation, and could cause
issues with the pilot not having control after a long dive.

Thanks to Soren for pointing out the issues

See issue #305
Copter: add pre-arm board voltage check

Copter will not arm unless board voltage is over 4.5V