Code : Implement method returning maximum of two floats
Code : Add estimator for terrain height and focal length scale factor
Code : change to 22 state computation

This is an experiment that uses the terrain position estimate from the
2 state ekf instead of the 23rd state
Modifications to replay quad123.zip data

This uses flow sensor gyro rates for motion compensation
Flow sensor gyro rates are corrected for bias errors
Add common parameter for minimum range to ground
Add quad122a.zip results file and associated change to GPS stop time
Code : optimised processing for 2-state EKF
Code : fix array initialisation bug
miscellaneous script file updates
Update scripts used to load APM flight data
Merge branch 'optflow-wip' into optflow22-wip

* optflow-wip:
  Update scripts used to load APM flight data
  Miscellaneous matlab script updates
  Derivations : Add 2 state focal length and ground height estimator
  Derivations : Derivation of single state focal length scale estimator code
  Derivations : tidy up 23 state derivation