deprecate Builders

see issue #131
diff --git a/include/json/reader.h b/include/json/reader.h
index 68b3738..d2bd140 100644
--- a/include/json/reader.h
+++ b/include/json/reader.h
@@ -277,6 +277,8 @@
 
 /** \brief Build a CharReader implementation.
 
+  \deprecated This is experimental and will be altered before the next release.
+
 Usage:
 \code
   using namespace Json;
diff --git a/include/json/writer.h b/include/json/writer.h
index 5dffbe0..e81c245 100644
--- a/include/json/writer.h
+++ b/include/json/writer.h
@@ -75,6 +75,8 @@
 
 /** \brief Build a StreamWriter implementation.
 
+  \deprecated This is experimental and will be altered before the next release.
+
 Usage:
 \code
   using namespace Json;