Remove using std::XXX from headers

This is a bad practice to have using in headers because it pollutes the
namespace of any user of that header.
diff --git a/xmlserializer/XmlStringDocSource.cpp b/xmlserializer/XmlStringDocSource.cpp
index 12307f2..ec2d7e9 100644
--- a/xmlserializer/XmlStringDocSource.cpp
+++ b/xmlserializer/XmlStringDocSource.cpp
@@ -33,11 +33,11 @@
 
 #define base CXmlDocSource
 
-CXmlStringDocSource::CXmlStringDocSource(const string& strXmlInput,
-                                         const string& strXmlSchemaFile,
-                                         const string& strRootElementType,
-                                         const string& strRootElementName,
-                                         const string& strNameAttrituteName,
+CXmlStringDocSource::CXmlStringDocSource(const std::string& strXmlInput,
+                                         const std::string& strXmlSchemaFile,
+                                         const std::string& strRootElementType,
+                                         const std::string& strRootElementName,
+                                         const std::string& strNameAttrituteName,
                                          bool bValidateWithSchema) :
     base(xmlReadMemory(strXmlInput.c_str(), strXmlInput.size(), "", NULL, 0),
          strXmlSchemaFile,