Fixed rover autopilot swerving when target heading is due north (#106).

The fix makes the AP use the instantaneous vessel heading instead of the moving average one. This may make the controller less smooth, but in the worst case we should be able to deal with that by retuning the heading PID controller.
Merge branch 'dev' of https://github.com/MuMech/MechJeb2 into dev
Fixed ascent AP inclination field not saving (#101).
Fixed a problem with dV simulation (#81, wasn't handling fuelCrossFeed = false properly).
slightly improved KillHS for heavier crafts
Merge branch 'dev' of https://github.com/MuMech/MechJeb2 into dev