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/assertions.h b/include/json/assertions.h
index 20716b0..9d93238 100644
--- a/include/json/assertions.h
+++ b/include/json/assertions.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_ASSERTIONS_H_INCLUDED
-#define CPPTL_JSON_ASSERTIONS_H_INCLUDED
+#ifndef JSON_ASSERTIONS_H_INCLUDED
+#define JSON_ASSERTIONS_H_INCLUDED
 
 #include <cstdlib>
 #include <sstream>
@@ -56,4 +56,4 @@
     JSON_FAIL_MESSAGE(message);                                                \
   }
 
-#endif // CPPTL_JSON_ASSERTIONS_H_INCLUDED
+#endif // JSON_ASSERTIONS_H_INCLUDED