Remove 'using namespace std' from SerialTypes.h

This unfortunately cuases a ton of flow-down changes because a lot of other
code was depending on that definition existing. This has a fairly large chance
to break builds of external plugins, considering how many internal ones it broke.

src/threading/formatters/Ascii.cc

@@ -9,6 +9,7 @@
 #include <sstream>
 #include <errno.h>
 
+using namespace std;
 using namespace threading::formatter;
 
 // If the value we'd write out would match exactly the a reserved string, we