StreamWriter: add a PutChar method to write a single char.

include/assimp/StreamWriter.h

@@ -203,6 +203,12 @@ public:
         Put(n);
     }
 
+    // ---------------------------------------------------------------------
+    /** Write a single character to the stream */
+    void PutChar(char c)    {
+        Put(c);
+    }
+
     // ---------------------------------------------------------------------
     /** Write an aiString to the stream */
     void PutString(const aiString& s)