Added path manager module. The path manager's function in the navigation
hierarchy is to pass the appropriate path segment to the path follower, and
monitor the path follower's progress.

Several new functions were introduced into misc_math. These functions
calculate certain geometries which are useful for dubins paths.

Lastly, three sample paths were provided. 1) A return home, 2) a position
hold, and 3) an example path that can be used as a base for further
path programming.
Removed path planning elements from manualcontrol.c.
Refactored path planner. The path planner's role in navigation is to take
user-defined waypoints and provide a path that connects them together.

The path planner is supplied with two algorithms, "direct" and "direct-
with-filleting".

"Direct" goes directly to the waypoint, no matter how severe the
angle between two consecutive waypoints.

"Direct-with-filleting" adds fillets
to the direction changes, in order to provide smoother, more realistic
paths for dubins cart vehicle classes, i.e. vehicles that have a minimum
turn radius.
Added circular moudulus for radians.
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.