Fixed Doxygen comments

src/blackmisc/blackmisc.h

@@ -1,11 +1,17 @@
-#ifndef BLACKMISC_H
-#define BLACKMISC_H
+#ifndef BLACKMISC_NAMESPACES_H
+#define BLACKMISC_NAMESPACES_H
 
 // just a dummy header, namespace documentation will go here
+/*! \file */
 
-/**
- * @namespace Aviation
- * Aviation and Avionics classes such as CHeading or CTransponder
+/*!
+ * \namespace BlackMisc::Aviation
+ * \brief Aviation and Avionics classes such as CHeading or CTransponder .
+ */
+
+/*!
+ * \namespace BlackMisc::PhysicalQuantities
+ * \brief Classes for physical quantities and units such as length, mass, speed.
  */
 
 #endif