Apply corrections from the "include what you use" tool

Generally cleanups of the includes. Making sure each file
can properly stand on its own and forward declares when possible.

include/chaiscript/dispatchkit/bad_boxed_cast.hpp

@@ -7,8 +7,15 @@
 #ifndef CHAISCRIPT_BAD_BOXED_CAST_HPP_
 #define CHAISCRIPT_BAD_BOXED_CAST_HPP_
 
+#include <string>
+#include <typeinfo>
+
 #include "type_info.hpp"
 
+namespace chaiscript {
+class Type_Info;
+}  // namespace chaiscript
+
 namespace chaiscript 
 {
   namespace exception