AP_RangeFinder: Added a new PX4 range finder and modified the RangeFinder parent class to support having multiple devices simultaneously
AP_RangeFinder_PX4_test: Added an example sketch for the PX4 range finder
AP_RangeFinder_PulsedLightLRF: Updated the value to write to the register to trigger a measurement
AP_RangeFinder: Changes from the May 4th plane test flight
PX4 ROMFS INIT: Added starting the optional mb12xx sensor
AP_RangeFinder: Seperated the Backend driver functionality into a separate class
AP_RangeFinder: disable old rangefinder drivers 

these will be re-enabled when they are converted to the new class API
AP_RangeFinder: new rangefinder API ready for its first backend

the backends are setup to have just the minimum functionality needed
for a rangefinder, with all of the higher level logic in the
frontend. This should make writing a new backend easier
AP_RangeFinder: converted analog rangefinder backend to new API

this gets analog rangefinders of all types working
AP_RangeFinder: added SONAR_RMETRIC option

this allows correct support for non-ratiometric rangefinders such as
the SF/02
SITL: update simulated sonar support
Plane: updates for new AP_RangeFinder API
Rover: convert to new AP_RangeFinder API
AP_RangeFinder: have two instances on all platforms

rover needs two sonars for obstacle avoidance
AP_RangeFinder: convert the PulsedLight driver to new API

not tested yet
AP_RangeFinder: convert MaxbotixI2C driver to new API
AP_RangeFinder: removed old style analog drivers

replaced by generic analog driver
Copter: convert to new AP_RangeFinder API
AP_RangeFinder: convert PX4 driver to new API
AP_RangeFinder: added SONAR2_TYPE parameter

thanks to Allyson for noticing