fix Document::Parse(const Ch*) for transcoding

To allow for an UTF16-Document to Parse(UTF8),
the Parse() argument has to be UTF8-compatible.

include/rapidjson/document.h

@@ -1951,7 +1951,7 @@ public:
         \param str Read-only zero-terminated string to be parsed.
     */
     template <unsigned parseFlags, typename SourceEncoding>
-    GenericDocument& Parse(const Ch* str) {
+    GenericDocument& Parse(const typename SourceEncoding::Ch* str) {
         RAPIDJSON_ASSERT(!(parseFlags & kParseInsituFlag));
         GenericStringStream<SourceEncoding> s(str);
         return ParseStream<parseFlags, SourceEncoding>(s);