reader: export CharReader::Factory

Author: mathstuf

include/json/reader.h

@@ -268,7 +268,7 @@ class JSON_API CharReader {
       char const* beginDoc, char const* endDoc,
       Value* root, std::string* errs) = 0;
 
-  class Factory {
+  class JSON_API Factory {
   public:
     virtual ~Factory() {}
     /** \brief Allocate a CharReader via operator new().