Text output support added for quantity

src/include/units/bits/fixed_string.h

@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include <cstdlib>
+#include <ostream>
 
 namespace units {
 
@@ -68,6 +69,12 @@ namespace units {
       }
       return first1 == last1 && first2 != last2;
     }
+
+    template<class Traits>
+    friend std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const basic_fixed_string& txt)
+    {
+      return os << txt.c_str();
+    }
   };
 
   template<typename CharT, std::size_t N>