AP_Math: fixed example build
AP_L1_Control: added lateral acceleration interface

this will be used by the Rover code for steering
Rover: use L1 controller for navigation

this uses the AP_L1_Control library for rover navigation
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
Rover: use a default max turn g force of 2g
AP_L1_Control: use projected position for turns
fixup groundspeed
AP_Math: update location code to avoid float rounding

this avoids manipulating global coordinates as float variables. Using
a float reduces our precision from 1cm to about 70cm.

This also adds location_diff() which will be used in the L1 controller
to avoid global positions in floats
AP_L1_Control: avoid using float global coordinates

this increases the navigation precision of rovers using L1 control
down to the centimeter level
Rover: update for new GPS API
AP_AHRS: added get_position_lag() call

provide position lag to libraries
AP_L1_Control: adjust position for GPS lag

this should help for rovers
AP_L1_Control: removed _maxf() and _geo2planar() functions

not needed any more
AP_L1_Control: use get_position()