EKF: remove dependecies and allow ekf to be built as standalone shared lib

EKF/mathlib.cpp

@@ -0,0 +1,14 @@
+#include "mathlib.h"
+
+float math::constrain(float &val, float min, float max)
+{
+	return (val < min) ? min : ((val > max) ? max : val);
+}
+float math::radians(float degrees)
+{
+	return (degrees / 180.0f) * M_PI_F;
+}
+float math::degrees(float radians)
+{
+	return (radians * 180.0f) / M_PI_F;
+}