First major wave of PQ refactoring, including but not limited to:

* Default unit is more clearly stated in one place, not restated in many different places, and is not always the SI unit
* Converter strategy pattern in CMeasurementUnit, covering linear, affine, and different kinds of sexagesimal units
* General reorganization of CMeasurementUnit construction and CPhysicalQuantity methods, not removing any behvaiour
* Move duplicated method unitFromSymbol from derived classes into base class CMeasurementUnit
* For DBus, CPhysicalQuantity marshals both in its own unit and in the default unit

src/blackmisc/mathematics.h

@@ -6,6 +6,7 @@
 #ifndef BLACKMISC_MATHEMATICS_H
 #define BLACKMISC_MATHEMATICS_H
 #include <QtCore/qmath.h>
+#include <cmath>
 
 namespace BlackMisc
 {
@@ -70,6 +71,26 @@ public:
      */
     static double roundEpsilon(double value, double epsilon);
 
+    /*!
+     * \brief Nearest integer not greater in magnitude than value, correcting for epsilon
+     * \param value
+     * \param epsilon
+     */
+    static inline double trunc(double value, double epsilon = 1e-10)
+    {
+        return value < 0 ? ceil(value - epsilon) : floor(value + epsilon);
+    }
+
+    /*!
+     * \brief Fractional part of value
+     * \param value
+     */
+    static inline double fract(double value)
+    {
+        double unused;
+        return modf(value, &unused);
+    }
+
     /*!
      * \brief PI
      * \return