Merge James's controllib bits into a separate library module.

Add a top-level mathlib header to avoid having to dig around for specific headers.

apps/mathlib/math/Dcm.cpp

@@ -37,7 +37,7 @@
  * math direction cosine matrix
  */
 
-#include "test/test.hpp"
+#include "math/test/test.hpp"
 
 #include "Dcm.hpp"
 #include "Quaternion.hpp"