Implements fall back to runtime simplification of unit strings

Compile time simplification of suffix string involves recursion for
partial specializaiton template that is not supported byt the current
C++ standard. The library come now with both Compile time support and
Runtine support for suffix formating. Static Suffix() method returns the
Compile time form (not simplified in all cases) while GetSuffix()
virtual method return the runtime form (simplified in all case). Both
methods take into accound kg special case.