Fix being unable to compile using clang version 10

libmandel/include/Fixed.h

@@ -13,6 +13,7 @@
 #include <array>
 #include <vector>
 
+#include <boost/serialization/nvp.hpp>
 #include <boost/multiprecision/cpp_int.hpp>
 #include <boost/multiprecision/cpp_bin_float.hpp>