surface: Added F15's elevator motion.
surface: Add F15's rudder motion
Convert EOL style of libmotion.h to LF for the next commit
Fix libmotion.h fail to compile with Linux gcc since 58947a
surface: Re-activate atmospheric pressure query in Aerial.
surface: Add landing gear model and motion to F15.

You can expand or retract the gear with G key when controlling a
F15.
surface: Shown landing gear status on F15's HUD.

Also, the aerodynamic drag take the gear into account (factor should
be tweaked, though).
Merge remote-tracking branch 'p-hd2/motioner' into motioner