Copter: update version to 3.1-dev
Copter: add SPORT mode
Copter: SPORT to use YAW_HOLD
Copter: Acro add rate constrain and combine limit calc
Copter: rename ACRO variables
Copter: Acro trainer separated into limited and leveled
Copter: Acro Trainer added to Ch7/Ch8 switch
Copter: remove ACRO's axis enabled parameter

Acro is now body frame (with earth frame leveling) while Sport is earth
frame acro
Copter: split ACRO_P into ACRO_RP_P and ACRO_YAW_P
AC_Sprayer: first implementation
Copter: integrate AC_Sprayer
AC_Sprayer: turn on/off the spinner with the pump
Copter: Sprayer enable added to CH7/CH8 switch
Copter: move CIRCLE_RADIUS definition
Copter: SPORT mode to use alt hold
Copter: configurable max lean angle

ANGLE_MAX parameter allows limiting the roll and pitch angles during
manual and auto flight modes to anywhere from 10 to 80 degrees
Copter: angle limiter fix for max lean angle
Copter: Leonard's sport fix re slow roll
AP_L1_Control: added lateral acceleration interface

this will be used by the Rover code for steering
AP_L1_Control: use a better ground speed estimate at low speeds

this should prevent a rover going in the wrong direction at the start
of a mission