Refactored fixed-wing path follower to use math from known good version.
Added UAVOs to Navigation category.
Added support for new navigation chain to FlyingF3 target. An option was
provided to easily disable the path planner.
Added library for computing atmospheric conditions.
Exported path followers to library.
Added path follower and atmospheric math libraries to FlyingF3 target.
Changes requested in review:

1) More (and better) documentation
2) Remove typedefs
3) Change sign() to SIGN()
4) Several other formatting and minor changes
Changes requested in review:

1) Improved comments and formatting
2) Removed unused callbacks
3) Used library circular modulus function
Slightly refactored find_arc_center in order to place the calculated center
at the end of the list, instead of confusingly in the middle.
Moved path manager switching algorithms to library.
Removed path planning elements from ManualControl module.
Fixed UAVO xml formatting issues. Also improved HiTL comment and random
number generation.
Changed int to uint16_t in for() loops.
Fixed ALL_DIGNOSTICS typo.
Fixed spacing aroud {. Also added a static keyword to processWaypoints()
declaration.
Fixed switch()..case: whitespaces.
Fixed citations.
Removed unnecessary includes of pios.h.
Renamed enum arc_center_results elements in order to avoid potential
namespace conflicts.
Removed unnecessary references to openpilot.h, in favor of narrowly
definining includes to the bare minimum.