Derivations : Adds airspeed and airspeed rate estimation
Merge branch 'master' of github.com:priseborough/InertialNav

# By Lorenz Meier (4) and Paul Riseborough (1)
# Via Paul Riseborough
* 'master' of github.com:priseborough/InertialNav:
  Change to a BSD 3 clause license
  Moved euler debug variables to mainloop, they are not part of the core estimator
  Commented required section back in
  Replaced the AHRS based init with a self-contained initialization for the sake of generality of the framework
  Updated readme for code to simplify execution of test environment