Doc: better reason for functions in type traits.

Also moved this to @internal instead of plain comment.

src/Math/MathTypeTraits.h

@@ -43,14 +43,13 @@ specialization for given types.
 This class and class methods are specialized only for types where it makes
 sense, it has empty implementation for unknown types or types which don't
 support given feature, thus forcing the compilation stop with an error.
+
+@internal The following values are implemented as inline functions, not as
+    static const variables, because unlike static const variables the
+    functions can be overloaded, deleted and hidden.
 */
 template<class T> struct MathTypeTraits {
     #ifdef DOXYGEN_GENERATING_OUTPUT
-    /* Development note: the following values are implemented as inline
-       functions, not as static const variables, because the compiler will
-       inline the return values instead of referencing to static data and
-       unlike static const variables these functions can return floats. */
-
     /**
      * @brief Epsilon value for fuzzy compare
      *