Issue 1100: Drop CPPTL support

CPPTL support is no longer relevant to JsonCpp, and can be removed from
the library. This patch removes all mentions of CPPTL, by removing all
definitions and code sections conditionally compiled only when JsonCpp
is used with CPPTL. Include guards are also renamed to not refer to
CPPTL where appropriate.
diff --git a/include/json/json_features.h b/include/json/json_features.h
index c12d647..a5b7305 100644
--- a/include/json/json_features.h
+++ b/include/json/json_features.h
@@ -3,8 +3,8 @@
 // recognized in your jurisdiction.
 // See file LICENSE for detail or copy at http://jsoncpp.sourceforge.net/LICENSE
 
-#ifndef CPPTL_JSON_FEATURES_H_INCLUDED
-#define CPPTL_JSON_FEATURES_H_INCLUDED
+#ifndef JSON_FEATURES_H_INCLUDED
+#define JSON_FEATURES_H_INCLUDED
 
 #if !defined(JSON_IS_AMALGAMATION)
 #include "forwards.h"
@@ -64,4 +64,4 @@
 
 #pragma pack(pop)
 
-#endif // CPPTL_JSON_FEATURES_H_INCLUDED
+#endif // JSON_FEATURES_H_INCLUDED