Autohover:
Improved lots of docs.
Cope with verbose display window sometimes not entirely being closed - it
seems we need to call .close() via a timer.
Created property gear/wow_any which is true if any gear is touching groune;
simplifies things because other parts of autohover can now use a listener
to detect landing, instead of polling.
Moved z-offset into global variable - no need for this to be a property.
Use property node objects to avoid looking up nodes via paths.
Changed autohover code to use a more consistent pattern where we have a
single listener which is called whenever state could be changed - e.g. by
wow or replay - and a timer to run the polling. The former can then decide
whether to call timer.stop() and close any relevent window.
Added nozzle-vertical, where we make nozles always point vertically,
regardless of aircraft pitch; makes it easy to do a Farley Climb. [Need to
figure out how to allow this to work with forwards-speed control.]
Fixed various issues with reloading autohover. We now initialise autohover
only if/when sim/signals/fdm-initialized is true to avoid problems where
we start too soon (e.g. with states). But this needs to be done at the
*end* of autohover.nas, otherwise if we are reloading autohover.nas, we
can initialise using some functions/data from the previous invocaction of
autohover.nas.
Other:
Changed controls/auto-hover/y-height to
/controls/auto-hover/y-height-target to be consistent with other
properties.
HUD now shows rotation info for both 'speed' and 'speed pid' modes.
