Reduce cost of including chaiscript.hpp

- ChaiScript no longer includes or automatically instantiates std lib
 - ChaiScript constructor now requires an std lib instance in the form
   of a ModulePtr object
 - This new layout facilitates better usage of compilation firewalls and
   factories for reducing the overall impact of ChaiScript on a project

unittests/functor_cast_test.cpp

@@ -1,4 +1,5 @@
 #include <chaiscript/utility/utility.hpp>
+#include <chaiscript/chaiscript_stdlib.hpp>
 
 double test_call(const std::function<double (int)> &f, int val)
 {
@@ -8,7 +9,7 @@ double test_call(const std::function<double (int)> &f, int val)
 int main()
 {
 
-  chaiscript::ChaiScript chai;
+  chaiscript::ChaiScript chai(chaiscript::Std_Lib::library());
   
   chai.add(chaiscript::fun(&test_call), "test_call");