Restore BL's authorship attribution, and add "The Jsoncpp Authors" where it was missing.

Requested/noticed in https://github.com/open-source-parsers/jsoncpp/pull/610, and a
followup to https://github.com/open-source-parsers/jsoncpp/pull/607 .
diff --git a/include/json/allocator.h b/include/json/allocator.h
index 2492758..9c7e573 100644
--- a/include/json/allocator.h
+++ b/include/json/allocator.h
@@ -1,4 +1,4 @@
-// Copyright 2007-2010 Baptiste Lepilleur
+// Copyright 2007-2010 Baptiste Lepilleur and The JsonCpp Authors
 // Distributed under MIT license, or public domain if desired and
 // recognized in your jurisdiction.
 // See file LICENSE for detail or copy at http://jsoncpp.sourceforge.net/LICENSE