added new sanity-check assertions

fixed issue with angles [bad interface]
- adjusted other parts accordingly
- added corresponding test-cases
started working on absolute heading

grid/walk/v2/modules/WalkModuleHeadingVonMises.h

@@ -81,7 +81,8 @@ public:
         const Heading stateHead = state.heading.direction;
 
         // get the error (signed difference) between both
-        const float angularDiff = stateHead.getSignedDiff(head);
+		//const float angularDiff = stateHead.getSignedDiff(head);
+		const float angularDiff = Heading::getSignedDiff(head, stateHead);
 
         // adjust the error.
         // note:	the error may get > +/- 2PI but this is not an issue!